From the delightful Wikipedia:

"The original U.K. and European cover depicts the Trifid Nebula in Sagittarius. The original U.S. and Canadian album cover (as released by Atlantic Records) was a Peter Sinfield painting of off-white with coloured "islands". This was used as an internal gatefold sleeve in the U.K. When the King Crimson catalog was re-issued by EG, they standardised on the "Trifid Nebula" cover world-wide.The original U.K. and European cover depicts the Trifid Nebula in Sagittarius. The original U.S. and Canadian album cover (as released by Atlantic Records) was a Peter Sinfield painting of off-white with coloured "islands". This was used as an internal gatefold sleeve in the U.K. When the King Crimson catalog was re-issued by EG, they standardised on the "Trifid Nebula" cover world-wide."

I've only ever seen the Trifid Nebula cover.