I THINK polybutylene is blue...
At least, that's what color the pipe coming into my house from the water main was. Whether it also comes in gray or not, I'm a big believer in "if it ain't broke, don't fix it" (that philosophy does NOT apply to preventive MAINTENANCE, however!!). Whatever it is, it's not leaking...even if it springs a leak, worst case: it drains your water tank into the bilge. So you have a wet bilge--which you prob'ly have anyway...it's not enough to sink the boat, and your bilge pumps will get rid of most of it. So scope out the sources for replacement materials--but don't buy 'em UNLESS/until you need 'em. Meanwhile, if you just have to make work for yourself, rebuild the toilet...it's prob'ly way past time to do that anyway, and that's one thing you DON"T want to wait till it's broke to fix it.