Yes, there are boundless ways to discriminate. Legally, most of them are irrelevant. We've picked a few well-defined things like race, gender, age, religion, marital status, etc. and said "These things you can't discriminate on". If you want to not hire someone because they wore a blue shirt and you hate blue shirts, you can do that.

Further, these aren't punished by force. The remedy is a civil lawsuit, not a criminal complaint.