i think its both ignorant and offensive. and although the two can sometimes coincide, racism and colorism are not the same thing, so thats why i didnt choose the third option.
im a huge believer in impact > intent, so regardless of whether or not what they were laughing at was a joke or not, colorism hurts individuals and entire communities and should be taken seriously. unless you're in that community, or affected by that issue, you should not be making jokes about it. like i always say, not your trauma, not your joke. so idols should not be poking fun at another idol who is darker than them.
theres only so much we can do as fans. to educate would be the best option, but there are obvious barriers to that happening effectively. speaking out about it on social media is really all that comes of it these days, rarely do groups/companies actually respond to the uproar.
but it's also important to keep in mind idols are not babies, they're (young) adults with access to google and capable of critical thinking. educate, but do not coddle.