My boyfriend and I have a policy, "your body, your decisions." Unless it's a health concern, you don't really have a say. It's just a beard. If it really looks that terrible, he'll figure it out on his own.

Rational Adult response: Tell him that the texture is really off putting and makes kissing him extremely uncomfortable and even painful from the beard-burn. (Yes, that is an actual thing.) Dickish and Passive Aggressive option: Assuming he takes showers, fill shower head with dye and glitter in his two least favorite clashing colors. Major Asshole option: While he sleeps, put something sticky and stretchy in his beard, like gum. Brightly colored would be even more effective. While two and three would probably have a higher success rate, they are obviously asshole things to do and could put strain on the marriage- well, more than it sounds like it is already- from you trying to control his body. Unless he nags you about your hair/beard/breasts/something-else- beard-equivalent-for-women, don't pester him about his. He might get bored of it or it might look and feel better once it grows out more. He can also condition it like one would condition the hair on top of the head to soften it and at least make the texture of individual hairs better.