One of our admins, HeypplsOfficial, has given us this code.

.comments li[data-user="User"] > blockquote { background: #color !important; } 
.comments li[data-user="User"] > blockquote:after { border-color: transparent #color transparent !important; } 
.comments li[data-user="User"] > blockquote div { background: transparent !important; }  
.comments li[data-user="User"] > blockquote {font-family:'Arial' !important;} 
.comments li[data-user="User"] > blockquote {color:#color !important;} 
.comments li[data-user="User"] > blockquote {font-weight: normal !important;}

Use this to be able to colour your speech bubbles.