I love your mod and would like to make a suggestion:

The filter used by the game engine to colorize the color masks is similar to Photoshop's "Overlay". This means that the color becomes purer each time the mask approaches medium gray (50%). When areas of the Mask are white, then the overlay makes the color whitish and when the mask is black, then this part of the color darkens.

So, for this appearance of overexposure in your mod to decrease, the ideal is to make the white areas a little grayer.

Look this test I did with a mask I edited in photoshop. On the left my mask, on the right your MOD.

https://i.ibb.co/8Pz4fDX/color-comparisson.png

If you need help with this, you can respond and I'll send you more balanced masks. But as I haven't bought the expansion yet, I don't have the original sloped locomotive masks.