Hi Natasha,

It depends on the sigma bond in question, but generally:

Sigma bonds have a relatively large energy gap between their bonding and antibonding orbitals, and because of E = hc/lambda, the wavelength must be small.

So most compounds with only sigma bonds appear white (think fats, butter tends to be quite white in colour) because they absorb in the X ray or even gamma wave level of wavelength.

Of course, you would have to do the calculation to know for sure.

Please let me know if this is unclear!

Katt