I can't remember how old I was, but I have a vague recollection that the first time I ever saw the puzzle now called Masyu it was labeled White Pearl, Black Pearl in GAMES magazine. I know it later went by just the name "Pearl" but at some point I could swear the two colors were separated out in the name like that. Wikipedia suggests that the name "White Pearls and Black Pearls" (in Japanese of course) was used for several years until an early misreading of the name by Maki Kaji eventually became Masyu, even if that name, meaning "evil influence", doesn't make a lot of sense. Today, I'd like to share another of my "Thomasyu" variations (the first being Total Masyu) that fits the name "White Pearl, Black Pearl, ..." pretty well.
In these puzzles, you will have to solve a Masyu by forming a single closed loop using the normal black/white circle rules. However, as in a well-patterned pearl necklace, you must also alternate between black and white circles when forming this loop. In other words, the loop cannot pass through two black circles or two white circles in a row. As you might expect, this introduces a lot more "avoid-self"-type loop constraints, but now between different loop segments.
While that twist might be fun enough, it seems reasonable to add in some gray circles (which must be a part of the loop and can serve the role of either black or white circles) with the same alternating color constraint. The loop can pass through two gray circles in a row, obviously, but it must alternate between the behavior of a black and a white circle in doing so.
But why use white and black at all? The rules of this variation should allow for a unicolor version. I can't reveal the true difficulty below, but it suffices to say, if I wasn't so bent on having a big ? symbol in the grid, it might not have ended up as hard.
Until the next Thomasyu puzzles, enjoy....