Dog Urine Color Why Clear Yellow Brown Orange Red
This is not a vet page so not from a medical source, but you can see - go to the vet immediately is the idea.
Males usually tend to get more issues with crystals and blockages so you never know what's going on.
I would have the urine checked, and a heartworm/tick test done unless he's had that recently done. I'd probably do a fecal while I was there, too.