Welcome FavesRBunny! That’s some great close-ups you got there. The fur here can sometimes get like this especially on bunnies carrying extra weight or have a dewlap. It can beome humid near the skin and the fur clumps. Sometimes a bacterial infection can develop. They have the scent glands under the chin too. Some bunnies are mad keen chinners!
My lop buck has this too. When I first got him he had a big pillow in his front (male dewlap I guess) and as he lost a little weight this area begain to improve but also became more visible.
If you notice wetness around the jaw, mouth also, then it could be more to do with dental problems, though as Sarita said, he seems too young for that.
The plant pigments can make urine red so if he’s been eating more grass, this may be why you’re seeing it more. It’s harmless. :o) Also when urine is exposed to air after a while it turns reddish. fyi: I just read on house rabbit society website also that first cold snap in fall can be one of the reasons to see more pigment in their urine. Never knew that!