Neon Orange ties?

I have been using paint washes on my track over the course of several days. A couple of interesting things popped out at me during the process. First, the gray ties are by and large a bad idea. They just don't look right when compared to pictures of the D&H mainline that I have. They might work in other areas of the country, but not here so I repainted them. My mainline is now a ratio of about 25% light brown ties, 24% dark brown ties, 25% black ties, and 25% Krylon camo brown ties. I like it much better.

Second, I noticed that as I used the washes more and more the light brown paint was turning orange on the ties once dry. It at first thought it was a fluke so I went over them again with another coat of light brown later on, but they they turned more orange. A day or so later, the dark brown began doing the same thing! I don't understand acrylic paints so I can't explain it, but day after day the amount of paint to water was slowly getting less and less. That shouldn't make it go orange though. I tried doing a black wash over them to look like the really rust-colored ties you sometimes see on sidings, but no dice. So, I made new batches of paint washes with much more paint and the problem went away.