Transparent Material Effect Color/Value on retopology mesh

Is it possible to set the color of the transparent effect that you can apply to meshes/retopology mesh.

I managed to change the material of my low poly retopo mesh to something like blue but when enabling transparent mode it switches back to a light grey. Is there a way to control this transparent color or value? Darkening it would be great somehow...

This tool makes the object look transparent without change its material.
View > Object Shading > Object Individual Shading > Transparent.
It is just an shading option. You may have tried this to apply material transparency.

The correct way to apply material transparency is
1. Set this option, View > Object Shading > Object Individual Shading > Solid.
2. Open the material window. Either "View > Windows > Material Window" or "View > Window > Material(Simple) Window".
3. Now click or double click the material you want to set transparency then set value in the the "Diffuse Alpha" field.