Lisbet, I apologize for my smart-aleck answer before. The 'hooch', as you call it [I like that description], is the result of the liquid separating from the solids in the starter. For the right consistency in your starter, and consequently in the finished product, stirring it back in or replacing it with an equal volume of other liquid, is the appropriate thing to do. However, understand that this liquid contains a good deal of the desirable flavors, live cultures and yeast associated with sourdough, and replacing it with something else will certainly affect the taste [and possibly the volume] of whatever sourdough you are making. In agreement with KYHeiloomer said, unless it smells really offensive, stir it in. And as for the odor...it's called "sourdough" for a reason, so expect it to smell sour... but if this makes any sense... pleasantly sour. I don't know what constitutes "discolored". The hooch on my soudough starter is typically very dark, but it isn't cloudy or moldy, so I continue to stir it in. If you continue using and feeding your starter, you can expect the sourdough flavors to develop more dimension over time. Unfed, they will go dormant, but will not spoil if stored properly [well covered and refrigerated] and will need to be "awakened" before you make your next batch of dough.
Here is a really good sourdough cookbook: "Worldwide Sourdoughs from Your Bread Machine" [Nitty Gritty Cookbooks] By Donna Rathmell German and Ed Wood. It explains everything about sourdoughs, heirloom yeasts, establishing and maintaining the culture, the history of sourdoughs, on and on. Yes, the recipes are formulated for bread machine, but they can be used with other methods too.
"The pressure's on...let's cook something!"