What Causes Bluish Discoloration Of The Toe Nails?

My big toes on both feet are turning dark blue black under the nails.
Saw a PA as one of the cuticals got infected but after 3-4 days of antibiotics has cleared up but under nail is still black blue.
glucose readings are 75 -122 as measured daily no swelling of ankles no discoloration of feet or toes no other symptoms of diabetes had physical 5 months ago all ok then blood sugar was upper acceptable limits.
Injured left toe and wore tight shoes one day that may have bruised left foot as well as aggravated left toe already black blue under nail.
have gout but no symptoms of that.

PA said did not look like fungus so what causes this turning of colr under just these two nails with no real pain no tingling etc.