There are 4 different areas of the silks that can be edited.
The jockey body palettes and jockey heads are in c:\program files (86)\starters orders 7\3D\race\jockeys - this is how the silks look in a race.
The pictures of the silks and helmets are in c:\program files (86)\starters orders 7\gfx\tables\bmp - this is how the silks look when you select them from the drop down menu in the game.
If you are going to try designing for yourselves, make a copy of the jockeys folder and bmp folder before you start, so if things go wrong, you can copy the originals back again.
I added my own silks and since there are 82 silks in the race, I created the following files:
Jockey_body_D_83.jpg
Jockey_head_D_83.jpg
483.png
1483.png
I you just want to change the colours of a set of silks already in the game, look in the two folders above and use "Paint" to change the colour scheme of the four relevant files.
If you are going to try designing for yourselves, make a copy of the jockeys folder and bmp folder before you start, so if things go wrong, you can copy the originals back again.
Have a look at the examples below, they might help you.
Have a go at it yourself, it's very easy. If you get stuck I will help you.
Jim