the pH is very important and effected in culture color, or maybe the seawater contain minerals effect on fungal color   

I agree with Oadi. 

Ofter fungi present different morphologies on different media, due to pH, C source and minerals (not to mention the presence of antibiotics and growth inhibitors).

It didn't happen anything strange to you (of course, I take for granted that you had not any contaminations, of course).

subculture green isolate back on to original media to check its not contamination 

I highly agree with Jane that you would better subculture the green one to original media and better check for the microscopic characters of the green one under microscope as well to double check  whether it is the same fungi you got before or not

...or sequence both white and green to check that the fungus is the same and that the color is determined by the medium-)

There are many fungi such as Trichoderma, Botryodiplodia, Aspergillus, Penicillium, etc etc show change in color in the culture media. We see the pigmentation as the fungus grow up with days and increase its growth and sporulate. Fungi like Aspergillus, Penicillium show color for the aggregation of the spores. Fungi like Trichoderma and Botryodiplodia show color change as the days pass, primarily for the production of spores. Botryodiplodia is reported to produce anthocyanin like compounds for pigmentation. So does Rhizoctonia.

To lend my voice to the nice comments above, your question is a little bit tricky but you need to know that most Aspergillus species show the green colouration due to sporulation. Sporulation as well as growth of the fungus is influenced by microclimatic factors (e.g. temperature, pH, media composition, Aw, etc.). When Aspergillus species begin growth, they usually show the whitish mycelia before sporulation. It is likely that the sea water (which has a different pH) kept the fungus at its mycelia stage or affected spore colour when produced while when transferred to the a more appropriate environment (MEA in fresh water) the typical growth characteristics showed forth. However, in line with Jane's comment, you could further make a subculture of the fungus from the two culture environments on reverse media (e.g. take the one in fresh water back to sea water and the one from sea water again to fresh water) and check for consistency. Sequencing, as suggested by Tatiania may further help to resolve the issues. It's a good thing you investigated into this and possibly, the mechanism. Good luck!

Its highly unlikely the strain will change colour if cultured in the same way. Please check it might be a contaminant. Reinoculate from the original stock. Keep the glycerol stock of the original fungal stain. That will help in maintenance of original strain. I hope that might work

In our lab we have also faced some issues with color changes of Aspergillus species when cultured onto the same media (malt extract agar), but of different suppliers... As we were checking formulations from many companies we found out that, even the different qualities of the malt extract used, could lead to different color result! I believe that, after excluding contamination, next to do should be the ph adjustment of seawater MEA medium to 7. If your fungus change again color, then probably is due to the production of some secondary metabolite whose production is favored on neutral ph. If the fungus retain the color that had in seawater MEA of initial ph, then is the media formulation itself that resulting to color differences.

Don't mind about color of the mycelium, try to grow fungi on different media and observed the morphotaxonomy, metabolite study and molecular taxonomy for the comparison of cultures on different media.

Fungi particularly the Ascomycetes and lower fungi changes color in different substrates. I reckoned that the seawater contributed significant changes in the MEA. Not to worry about the color. It is the spores that  are normally strongly pigmented, which implied that the seawater  probably promotes more sporulation.

Colour of the fungi depends on the type of medium and its pH, age of the culture and sporulation. That is why a fungus is studied on standard culture media for identification. Colour change on standard media has taxonomic importance. A fungus may have different colours on obverse and reverse; and may  produce diffused colour/pigment into the substrate medium.

What genus is your fungus? 

Thank you for all,

After I checked under the microscope, the conidia had a shape such as Aspergillus, it had vesicle. The mycelium is transparent and there is no  septum there. 

may be your culture into the reproduction phase? sporoulation may change the colour of culture?

Examine  your fungus  mycelium morphology  under microscope  through using different

media. Salinity affect mycelium morphology  but  did not  affect color   ,also pH 7 is not favourite pH  for Aspergillus sp try pH 5.5.

Mr Eman, the strain Aspergillus that I isolated getting associated with sponge in Southern Sea of Yogyakarta.

Here, I attach the picture that I got from the microscope observation

Gadjah Mada University, is a beautiful campus. I visited the scenic campus in 2007 attended Asian Plant Pathology Congress. With age, fungi produce spores, secret extracellular enzymes, toxins, anthocyanin and other pigments one of which is the cause of culture color. I have experience with Botrydiplodia, Colletotrichum, Phomopsis, Trichoderma, Rhizoctonia but no such working experience with Aspergillus.

Salinity can affect sporulation in fungi (e.g. http://link.springer.com/article/10.1007/BF00443842) and, as several people have mentioned, sporulation can be a factor in color changes in fungal cultures.

As a note, if your hyphae, not just the conidiophores, are non-septate, this is not Aspergillus.  There appear to be some septa in the hyphae in your picture, but it is not clear.  If the mycelium is aseptate, there are some zygomycetes that produce asexual spores on vesicles.  There is a good micrograph on the fungal tree of life website for zygomycota of one of these (Syncephalastrum) (http://tolweb.org/zygomycota).  I don't know of any that are green, but zygomycetes are not my area.

Thank you for the information,,, now, I am still cultivating my fungi for extracting the secondary metabolite.

Mrs. Linda E. Hanson, thank you for the link, it helps me well for correction of my fungi hyphae.

I will try to exact about the septum in hyphae. but, I get others, that this fungi has a brach in the hyphae

It is scietifically prooved that colour production in colonies of aspergilli and penicillia is dependent  on availability of metal ions in media like copper, Manganeese etc. possibly the sea water may lack such ions. the microphotograph shown above belongs to Aspergillus not syncephalostrum because later does not produce green color in any cercumstances. regarding unseptate  hyphal structures  in most cases conidiophores may be unseptate.

Fungi, particularly the lower fungi often give different color when cultured on different substrates. The addition of the sea water may introduce several nutrients not available in water. Therefore, it is rather obvious that the fungi changed color.

I think you must grow it again under salinity condition (sea water)and in fresh water

,then examined it under light microscope  to see  any change of morphological structure , colour change may be due to salinity stress .

Lower fungi are hyaline, some very particular one acquires pigmentation upon maturity. Sometimes their hyphae show septation too. My experience tells it is the higher fungi show pigmentation beginning growth such as Colletotrichum, Botryodiplodia, Pestalotiopsis, etc. Components of growth media always have influence upon fungal pigmentation.

you have to examine the white mycelia grown in MEA with sea water to see the mycelia if they are similar to Aspegillus but without conidia , so it is correct.

spore production will change the color(Extending life from asexual phase to Sexual phase.)

high pH or salinity or osmotic pressure all can affect the sporulation and growth of Aspergillus

interesting question and very good ansewer. thank you for the information

Good day to all.

A nice question, with valuable suggestion given.

Requesting to add some research article that could be considered for referencing.

Thankyou.

I have experienced the same..