It's hard to tell from the pic you posted, the cere looks normal to me.
Male's cere's will change a little bit during mating season to a slightly more prominent blue or purple colour. Now that spring is here, your budgie may be hormonal (even though he's well past breeding age)
The more concerning thing to me is his weight, he looks extra pudgy and definitely needs to lose a few ounces. What does he eat on a regular day? Does he get any out of cage time to exercise? Has he had a vet check in the past year?