Paint Matching
Paint a clean white piece of smooth posterboard with the Testors (or other prepared) color and bring it into a paint place that can color-match it - they're really, really accurate now.
Ideally, airbrush the Testors (or other) paint onto a flat white -very smooth- surface, such as a piece of glass or a sheet of rigid plastic. Spray about 6 coats to make sure there's absolutely no translucency.
Assuming the paint you're using isn't glossy, getting the finish as flat as possible for the paint scanner will yield the best results.
The best part about it is this - let's say your color comes out being off by a few percent. You'd never notice, because you won't be viewing the cockpit in perfectly even, prismatically-corrected light, and every surface this appears on will appear slightly different anyway!
Color Codes
Something from the simpits-tech mailinglist:
http://www.ipms-earth.com/fs595b/ Federal Standard 595B Colors
To get a Testors number from those Federal Standard Color Codes found in specs of panels and similar (eg. "Non-reflective Black FED STD 595b37038") read what Gene B. wrote on this topic on simpits-tech:
"You can get most or all of these colors from Testors. The important part of the number is the last 5 digits. For instance, the black is '37038' or 'FS37038' "
A few more helpful links regarding Fed Std colors and Model paints:
http://www.ipmsstockholm.org/colorcharts/stuff_eng_colorcharts_fs.htm Urban Fredriksson's Color Reference Charts Federal Standard http://www.ipmsstockholm.org/colorcharts/stuff_eng_colorcharts_us.htm Urban Fredriksson's Color Reference Charts United States http://www.ipmsstockholm.org/colorcharts/colorcharts.asp Urban Fredriksson's Color Reference Charts Part I http://www.ipmsstockholm.org/colorcharts/colorcharts_2.asp Part II
Try out some colors to get a rough approximation in your webbrowser:
http://www.ipmsstockholm.org/colorserver/showcolor.asp?fs=36440 this is the color used for Boeing's knobs (change the number in the URL to change different color code)
Mike also has some good infos along this line, esp. for the older BAC (Boeing Aircraft Colors) system:
The paint for a FOKKER 70/100 Cockpit whitch matches best an has the correst surface is: Multimix KF 700 Soft Touch Ral 7011 cost: ~80€/liter
A/C Types + RAL Color Codes
B737-800 RAL 7024 (also 7011)
Airbus ...