It is possible to obtain colorless filtrate for mixed ligand metal complexes, depending on the specific composition of the complex and the conditions of the synthesis. Some metal complexes have a yellow or brown coloration that can be difficult to remove, while others can be synthesized in a colorless form.

In general, the formation of colored species can be influenced by a number of factors, including the nature of the metal ion, the nature of the ligands, the pH of the reaction mixture, and the presence of impurities. In the case of mixed ligand metal complexes that contain a carboxylic acid ligand, the formation of a colorless complex may be influenced by the choice of solvent and the pH of the reaction mixture, as well as the identity and concentration of the other ligands present.

It may also be possible to remove any coloration from the filtrate by carrying out further purification steps, such as recrystallization or column chromatography. However, the specific approach that would be effective for a particular system would depend on the particular properties of the complex.

If a complex absorbs light in vis-range, you can't make it colorless without destroying it.

It isn't that I want to make the filtrate colourless. As widely known, the filtrate for the complexes of the said metal ions(Cu, Ni, Co) should be coloured. But in my own case I have been getting colourless filtrate all along. I want to know if this is normal or there is a problem with my reaction.

You did not provide any details, it could be whatever.

Hassan Kehinde Busari If you meant by "Colourless filtrate" Colorless solution after filtration of your formed complex (powder)

This would indicate that all the quantity of the metal ion that you have added, reacted or coordinated with your ligand (yield ≈ 100%), which is quite hard to realize and highly dependent on the metal/ligand ratio.

Otherwise, which type of filter paper are you using ? some filter papers can adsorb solutions, try to check if the expected color is in it.