Iron has no white (colorless) salts or other compounds. This is the property of element Fe (d-element). So, colorless Fe2+ solution exists only at very low concentration.

Solutions of ferrous sulphate (‖) under the action of oxygen dissolved in water, gradually oxidized, passing into iron sulfate (|||):

12FeSO4 + 3O2 + 6H2O → 4 Fe2 (SO4) 3 + Fe (OH) 3 ↓

The trivalent iron ion gives a color. To avoid oxidation, nitrogen must be passed through the solution or argon.

I agree with both answers, additionally the solubility of Fe(II) and Fe(III) species depend on the pH of solution. At pH >1.8, these species may precipitate out and the solution concentration may be very different than expected. The greenish color and yellowish green color associated with the Fe(II) and Fe(III) species , respectively (in acidic conditions and considering Cl- or HSO4(-1) and/or SO4(2-)) is due to the inner d-shell electron transport process when these adsorb light of specific wavelength. So under natural conditions it is hard to vanish the color associated with these species. Probably under some specific conditions (under exposure to specific wavelength radiations this may appear colorless, which i am not sure and have no experience.

Dear Nima Jafari ,

It would be better if you clarify your question in a better way- do you require a colorless Fe(II) or Fe(III) ion aqueous solution? Is the anion/ counter ion very important for your study? The color of Fe(II) or Fe(III) ion solutions depend much on the nature of associated ligand as well. Accordingly, it can be modified!

Sorry for the duplication of my answer. This was unintentional and was caused by my computer malfunctioning. Sorry for any inconvenience.