The coloured solution (S) contains: Fe2(SO4)3, ZnSO4, CuSO4, Na2CrO4

The filtrate contains Cr(III) ions which reacts with ammoniacal H2S to form green ppt. of Cr(OH)3↓. This ppt. dissolves in aq. NaOH/H2O2 to form yellow colored Na2CrO4. Thus, the coloured solution S contains yellow sodium chromate Na2CrO4.
Cr3+ + 3NH4OH + H2S → ammoniacal medium Cr(OH)3↓ (Green)
2Cr(OH)3 + 3H2O2 + 4NaOH → 2Na2CrO4 (yellow color) + 8H2O