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.

I may have gone a bit overboard, I know how the masks work, I can tone them down a bit. However, I was thinking that you can basically achieve the same thing by setting the train color to a smaller RGB value. This will get rid of the “overexposure” look, while still allowing other players to enjoy the super-saturated look, which I can imagine some people actually do like.

Maybe I'll just add the less saturated sprites as well and make it selectable in settings which version you'd like to use.

But that's for tomorrow.

Created settings for choosing the saturation level.

Here is the comparison:
https://ibb.co/Lg8FKBR

The bottom one (old) is the super-saturated look, the top one is the more natural look.