I will give a few questions that I hope helps out:Magikarpmaster629 wrote:The way I understand color-color diagrams is that they compare the fluxes of different wavelengths in the form of a graph. If that's the case, then why can't we just use the blackbody curve, which gives us fluxes at all wavelengths?
1) I presume by blackbody curve you might mean a spectrum. Spectra include blackbody curves, but blackbody spectra aren't the only type. A simple way to describe this is by "Kirchoff's Spectroscopy Laws" if you want a simple comprehensive way of thinking about it (I figure you knew this, but I might as well mention it).
2) Are spectra easy to get? How do we get fluxes, and how do we get spectra?
3) Say you did photometry and made just a batch of flux measurements. How easy would it be to quantify certain spectral features if you just plotted it on a graph as a function of wavelength? This is a useful method, but are there cases where you expect some behavior that you can quantify by comparing fluxes? Hint: Think about all the different spectral features there are. Also, they're useful for the same reason you use color-magnitude diagrams to classify stars.
I think that may define the questions better. Does that help? The summary is certainly it'd be nice to have better data, but can you always realistically? A super important thing is astronomers have gotten pretty good over the times with this exact issue of getting a lot of information from few observations, and color-color diagrams are an example. Note this is mostly just explaining the "why bother", not necessarily the how it's used, which might also be enlightening to get ideas.