What Causes Spots On Chest And Stomach?

My 9 month old just had blood drawn to test for a petechial rash, (we haven't got the test results back yet). The spots are on her chest and stomach area and do not spread but seem to get lighter and darker from day to day. The do not change color when you apply pressure. Is it possible for petechial rashes to look darker some days? What other things could this be? Any suggestions?