I just got it. I did my hrv. My readness say 0 and has no colors, does it only give me readings after it has something to compare i too.

Yes, and the more readings, i.e., daily is the best, the more accurate your readiness reading will become.  Did you follow the recommendation to take your initial readings somewhat rested (stress free as possible, good nutrition and hydration) for about three days?  This helps establish a baseline that is a bit more representative of your HRV if I understand correctly.