I'm guessing the light and dark splotches are normal pied pigment variations that you see on his cere. But I've noticed a yellowish tinge around the nostrils. Is that normal? He seems healthy and happy. He's my little sweetheart, Dave.

the pied mutation can also play fun and games with the cere, especially of Double Factor Dominant Pied as well as recessive pieds.

Yep it is normal.