Color was pictures plus location, that's true. Instagram is also just pictures and filters, which is equally dumb but turned out pretty well from an investor's point of view.
However, you make a good point. Neither Color nor Instagram were/are "sustainable businesses". Sequoia just wants a return. Google is a sustainable business, and if you build one, Sequoia will get their return. You can also just get a bunch of users and flip it to Facebook. They'll get their return then too. And I'd bet Sequoia doesn't really give a crap which way you do it.
It may be and your might have encountered an exception(s), but as whole the venture industry has clear economic drivers and generally people's behavior matches the underlying incentives.
Of course, my point excludes the examples of non-ethical behavior.
However, you make a good point. Neither Color nor Instagram were/are "sustainable businesses". Sequoia just wants a return. Google is a sustainable business, and if you build one, Sequoia will get their return. You can also just get a bunch of users and flip it to Facebook. They'll get their return then too. And I'd bet Sequoia doesn't really give a crap which way you do it.