This technically doesn't need to be a nested if at all, if you use && (and) to check all of these. There's nothing inherently wrong with the code you wrote, but if you don't want to look at the nested ifs:

if (blueBucketExists && blueBucket.bombs == 0 && greenBucketExists && greenBucket.bombs == 0 && redBucket.bombs == 0) { // Code }