... I can bet that it is tough to match the loco color...
Here's a sample set of color swatches I used:
First, I [digitally] photographed a brightly-lit surface area of the paint color I wanted to match, uploaded it to my PC, then opened the image file with a Photoshop "wannabe" graphical editor.
Next, I zoomed into the part of the paint I wanted to imitate, clipped a square of that and pasted it to another corner of the photo image, then noted the R/G/B values (Red/Green/Blue color components).
Then I made 4 copies of the swatch, made each one progressively lighter, and
noted
their RGB values.
Next, I copied the set of 5 blue squares into a new image file, printed that on white decal paper, then sprayed it with decal bonder. (This is
very important, in order to see what the decal will look like with the protective sealer on - usually somewhat darker/deeper than without it.)
After the decal bonder dried, I held the swatches up against the painted surface I wanted to match, noting the RGB values of the closest matching square.
Returning to my graphical editor, I set the background color to the selected RGB values, and -
voila! - decals.
Hope this helps, I probably need to write-up a more detailed version of this process (including more pix)...
Good luck!