How to filter lookup field from parent lookup field

How to filter lookup field from parent lookup field

Hi,

I've set 2 forms which are depended.
Form A : list of materials (singletext field Materials)
Form B : list of all colours (singletext field colour, singletext field material)

the singletext field material in Form B, is for now a comma separated list : "material 1, material 2, material 3"

In a third form C, I like to select a material from a look up field and then select colours. But I only want to filter colours that are available for that material.
note: one Colour may be available to multiple Materials

For example:
- Material A allows Colour 1 and Colour 2
- Material B allows Colour 1 and Colour 3

How I can filter the colour lookup field (in form C), based on the selection in Material Look up. Any ideas ?
May be the 2 lists Materials and Colours are not set correctly in Creator. Let me know.

Regards