You can use the "COLOUR_CHANGE" command in a lnc file to change kit colours in save games (changes will take affect in the future matches).
If you browse to:
\Football Manager 2007\data\db\700\lnc\all (If you are using a different database you may need the file in the equlivent place)
Now open one of the lnc files with notepad, and paste this line into the file, doesn't matter where:
<pre class="ip-ubbcode-code-pre">"COLOUR_CHANGE"6881A1A2A3B1B2B3</pre>
First you'll need to edit the line:
688 - is the ID of the team (688 is Newcastle's ID)
1 - Tells the game to change the Away Kit (0 - Home, 2 - Away)
A1 A2 A3 - Controls the colour of the text (players number on the pitch) for that kit, A1 amount of Red, A2 amount of Green and A3 amount of Blue (numbers range from 0-255, so blue would be 0 0 255).
B1 B2 B3 Controls the colour of background (dot colour, shirt colour) again same as above B1 - red, B2 - Green, B3 - Blue.
(White is 255 255 255, Black is 0 0 0)
So if you wanted a white away kit with black text you'd change the code to:
<pre class="ip-ubbcode-code-pre">"COLOUR_CHANGE"6881000255255255</pre>
To get an RGB code for your colour open what ever imaging program you have select the colours you want, and the program should somewhere give you an RGB value for the blue you want.
Hopefully sometime in the future (If Ter gets chance

) we'll be also able to edit the trim/third colour and kit style.