The other's (@TangHo's) answer seems to make sense. I'd like to add a few more comments/explanation.
Within this context, 景色 seems more like a "scene", i.e., "(many people riding) Bicycles have/has almost become a major scene of the city." It's in the same way like something relatively common (such as wild flowers), but when on a large scale (满山遍野的野花，wild flowers all over the mountains/hills), becomes something worth taking a look (i.e., a scene, or if more striking, spectacle).
In this sense, 景色/景致/景观 are probably similar with subtle differences/emphasis; I would prefer using 景观 here, i.e., 自行车差不多成了城市的一大景观。
My feeling is that 景色 does not have to be as striking as what a spectacle means, and in that sense I'd rather translate it to "scene" (or any english native speaker can suggest a better word for something worth a look but less striking than "spectacle"?