Is the Sun slightly blue in the center? - Wavelength-dependent limb darkening of the Sun
You might find this paper helpful:

http://www.physics.hmc.edu/faculty/esin/a101/limbdarkening.pdf

Look specifically at Eq. 5 for the wavelength dependence.  To get the intensity, use Equation 1.  The value of $u$ can be found in the caption to Figure 2.