thank you for asking! similar to commercial coffee mugs, if you leave colored liquids in them for a long time, like coffee or tea, it will leave some stains. if you wash them in a timely manner, the stains should be easily removed. i personally drink tea out of them daily, wash them immediately after and have had no staining issues.
if heavily colored drinks are regularly left in them for long periods of time, there is potential for permanent staining, as is the case for commercial items as well. i hope this helps!