Hello, pure colored parts have a glow that makes them look whiter than #FFFFFF textures.
Here's a refrence:


Left is #FFFFFF, right is pure.

On the other hand pure gradients won't fix your problem since applying a texture voids the gradient entirely.
You won't be able to match pure with #FFFFFF textures.
One solution might getting off white colors that match better with these textures such as impure or ivory.
Here's a list of all colors: https://forum.toribash.com/showthread.php?t=647523
Another solution is to buy joint textures and match them accordingly.

Hope this helped, sorry for the inconvenience.