In this case, there are the four Turtles, Splinter, and one other potential Commander with Partner thats yet to be officially revealed (though it seems like its almost certainly a version of April ONeill), each with a single color
If the target creature is an illegal target, you'll still gain control of the target Equipment until end of turn, but you won't attach it to the chosen creature
Permanents that allow you to tap your lands for any color, like Cromatic Lantern and The World Tree, make it easier, but if you don't have access to these permanents early, you may be stuck on having the wrong lands for what's in your hand.
Players can find a full description of character cards on page 5 of the rulebook
Paying attention to the manufacturer, release date, and specific product line can help you find rare or limited-edition sleeves that may become highly sought-after over time