Press the "Esc" key, scroll down and click on "My Realflight", from the that drop-down list select "Save Color Scheme As", give the new color scheme a name, I just called it "B-25 Color" (see pic#1)
The color scheme (TGA) gets saved in C:\Users\Your name\Documents\Realflight Evolution\Vehicles\Color Schemes, (see picture#2)
Open the B-25 Color.tga file in your editing software, change the colors and save the TGA file, confirm overwrite, and be sure to save as a 32 bits/pixel.
As you can see I used colors that are "Vivid" just as an visual example. (see pic#3)
Now go back to RF Evolution, select the B-25 and notice the Color Schemes Icon (see Pic#4) will have changed from greyed out to blue background, click the icon and select B-25 Color, (see pic#5)
The B-25 appears with its new colors.