Usually , ferrous sulphate is soluble in water without any coloration . If you are getting yellow color formation , just treatment the solution with activated animal chorcoal and filter it , likely that you will get colorless solution or else you can use deoxygenated water while dissolving ferrous sulphate....

I agree with Anoop Kumar Srivastava .

I think that the problem is the water used to disolve your iron(II) sulfate

I agree with Anoop Kumar Srivastava .

Most of the sulphates are soluble except Ca+2, Pb2+ and Ag+

Check if you could consider to substitute Mohr's salt (ammonium ferrous sulfate) for the less stable ferrous sulfate (aq. sol.):

http://pubs.rsc.org/en/content/articlelanding/1987/an/an9871201743#!divAbstract