Firstly, let me just say that I adore Sharpie markers.
It may be a strange obsession, but I love writing with them.
Naturally, being a... Sharpie lover (?) I was drawn to this photo.
I really like the color progression; the way you have arranged the colors is nice because it doesn't make one color stand out more than another - the eyes follow the colors themselves from one side to the next.
I like the bubbles, and how they aren't exactly identical but quite similar.
With that being said, I think it would be interesting to see the markers lined up in a way that isn't straight across. Perhaps if they were lined up like... well (utilizing this key on my keyboard that I never do): ~ rather than - (I hope that makes sense).
I just think that seeing them arranged uneven would be interesting.
Also, it may be fun to mismatch the bubbles so that the bubbles don't match the marker they were drawn with. Just throwing out ideas, because I do like the theme of this.
Well done!