At real site or STP that I had visit, the color of ML activated sludge should be dark brown or black. But if you refer to ML activated sludge in laboratory, the color will change according to type of substrate that you used. 

Need a little more information as to how many times you have run a start up sequence on this SBR or if your refering to every time you start a new one,  and what is your source for the activated sludge biologicals because that usually will answer a great many things in any liquor color, consitancy, foam color as well as it's odor.

Orange to red toned color is usually a sign of higher Ferric/Iron usage or content which stains the foam and liquor or in the case of some strains, it stains their cell wall or nucleus as they uptake the iron. In the case of a sludge containing high numbers of uglena, they have a red "eye" and in larger numbers tint the sludge. But that usually ends up red not orange.

Cream or white colors I have only ever seen in aerobic basin foam and it indicates a normal start up or a very high BOD loading with a matching high F/M ratio. This corrects itself as the sludge ages to a proper 5 day cycle and or you adjust the MCRT to 5-6 days. if it doesn't correct after startup then you'll need to look at RAS and WAS settings to see if you need to waste out more sludge or retain it just a little bit longer to prevent shock loading.

If your infleunt is cream/orange and you haven't just dosed large amounts of chlorine with a strong ferric presence in order to mix and become cream orange... then I'm not able to advise on that one.

Lastly you can having a great many colors in your sludge based on the influent quality and source. Industrial will range from every color possible because you'll see so much more than heterotrophs and domestic loading. I've had bright purple from beets, yellow from tumeric, blue from portopotties and green from heavy algal based influents.

As always always always (which in life is rare) you've got to know where your microbes for startup came from as well as knowing what's in your influent so you can best adjust for treatment. If your seeing the same results during each startup of multiple SBR then based on your equal startup parameters, well this may just be normal for you so there isn't anything wrong or in need of correction. So there is plenty that you'll need to test and compare to know if it's based on what your doing or what your receiving.

In a properly running domestic waste aeration basing be it a WWTP or SBR you want the liquor to look like chocolate milk and smell like clean dirt. That's when you know from sight and smell alone that your ratios are where they belong and your microbes are happy and healthy.  Once it turns dark brown or black you'll gain H2s odors and risk septicity and shock loading which in an SBR can only be corrected chemical at that point. because time rarely permits a biological solution correction.

So if you want to narrow things down we'll need a little more information from you and your influent makeup.

If it is lab reactor, may be due to Iron or even the organic substrate you use.

Usually it depends on the types of your sample i.e activated sludge/POME etc.

The DO in the reactor. High DO -yellowish/orange. Low DO-dark brown

Orange to red toned color is usually a sign of higher Ferric/Iron usage or content which stains the foam and liquor or in the case of some strains, it stains their cell wall or nucleus as they uptake the iron.

In the case of a sludge containing high numbers of Uglena, they tint the sludge as they have a red "eye" . But that usually ends up red not orange tint.