Usually, yellow tan or gold color indicates extra colostrum and the milk is very rich. But, typically, you see that in them when they are 3-6 days old and it is very sticky.
Give him 1-2 Sustain boluses (1 for less than 100 pounds, 2 for 1-200 pounds, they are blue pills). That will stop the runs. Waiting until they are lathargic or depressed is too late - they are very dehydrated at that point. Boluses are giant pills, oral antibiotics. You will need a pill pusher, too. Your vet, co-op, or feed store should have what you need and buy the pills individually - don't buy that big huge jar.
If it turns brown/green or grayish white, treat ASAP - it is e-coli, which will kill them quick. You'll need to retreat 48 hours later. If it is real bad, you can also give a 6 cc shot of Nuflor, SQ. If you've had a lot of rain or moisture lately, that very well could be the case.
I just treated all my calves less than 6 weeks old for e-coli - and every one of them was very lively, but squirting everytime they stopped moving.