Please hear me out before telling me 'just add back warmth'.

  
Basically, imagine you have a shape where you laid out the base color. e.g, made with a mix of dark sienna and UM blue with a tiny bit of titanium white for added opacity.

 Then, you want to paint the lighter part that's hit by the light - typically I would want it to be slightly warmer, and lighter in value.

So what I would do is take my base value, add zinc white, but often it's not enough opacity and will add a bit of Titanium white. Opacity is super important for my painting style because I paint animal fur hair layered on top of each other.

\- Here lays my issue: When I do that, the temperature will shift to a colder hue because of the whites. I try adding raw sienna to warm the mix again but it doesn't really work because it is being overpowered by the T White I guess.

But not using T White results in insufficient opacity...

 Haven't had much luck using a paste medium either.



I don't have this issue with oil painting. Anyone could provide guidance on this please ? I feel like I'm doing something wrong and my highlights end up too cold. 

See my picture here - you will see the speck of highlight looking bluer than the rest :,)





How do you lighten a color without losing warmth for high opacity painting ?