Do you believe in the existence of universals?

such as "redness". This is a universal. "roundness" is another example. There are tons of universals. "Skittleness" is the universal that all particular Skittle candies would exemplify. Or do you believe only in the existence of particulars? i.e. Nominalism. If so, what do you mean when you say two different things are red? A realist (believes in universals) would just say both objects are instances of the universal "redness". However, if you're a nominalist you can't appeal to any universals at all in your explanation of two things being the color red. So how do you explain this resemblance? What does it mean for two things to resemble each other?