Breakdown of tomodachi wa kabegami no tsuya to sashiiro o mite bakari iru.
Questions & Answers about tomodachi wa kabegami no tsuya to sashiiro o mite bakari iru.
は marks 友達 as the topic: as for my/the friend...
In a sentence like this, は is natural if the speaker is talking about what that friend is doing. It gives a descriptive, topical feel.
If you used が, it would sound more like you are specifically identifying the subject, as in the friend is the one who is... That is possible in some contexts, but は is more neutral here.
Also, 友達 can mean friend or friends depending on context.
