Q. My yellow roses were beautiful the first time they bloomed before Easter. However, the flowers aren’t pretty any more after they open. The flower looks burned on the edges of the petals. I haven't seen bugs on the flowers. Otherwise the plant looks healthy to me.
A. Your roses, from the sound of it, are probably infested with Western flower thrips. These are very small insects that are nearly impossible to see unless you use a magnifying glass and inspect the flowers very closely. They are also difficult to control.
Posting in pictures by Colorado MasterGardeners
Thrips damage on lots of things in Canada
Thrips are poor fliers and so stay close to the plants they feed upon. They have mouthparts that shred tender plant parts such as flower petals and flower buds before or after they open. The flower petals appear damaged and with streaks of brown.
Soap and water sprays are somewhat effective but the best to spray for controlling this insect contains Spinosad.
Dormant sprays of horticultural oil during the winter and applied before the plants start growing will also help. I would alternate sprays between an insecticidal soap such as Safer's and Spinosad sprays until you get some control.