Recommended settings for the Dell 2408WFP monitor:
Color Model: AdobeRGB (not sRGB)
R = 96, G = 92, B = 100
Values taken from these calibration results. The author notes "this is by no means a universal recipe as models vary," but I don't have the equipment to run my own tests and these settings look excellent to me.
If you want to calibrate the monitor yourself, see calibrating a Dell 2408WFP with Spyder Elite 3.