Discoloration in tea kettle I have a two piece tea kettle used for brewing black Turkish Tea. The bottom part is used strictly for water (specifically faucet water), whereas the top is for steeping the concentrate of the tea. 

Today I noticed some really odd discoloration on the lower portion of the kettle:

Here is an image of the lower portion of the kettle, reminder; this is only used for water, and this is post-cleaning

After some web searching I thought it was limescale so I boiled vinegar + water and cleaned it off with a rag and some baking soda, here is what the rag looked like after some scrubbing.

So my question(s) is; is this limescale? And if not, what is it? Is it fine to boil water in it like this?
Yes that looks like limescale. Are your water mineral rich?
Limescale comes in different colors depending on minerals in water. Mostly common, white, greyish or reddish. Iron. 

Vinegar may leave a taste, so you can considder to buy commercial descaler from the supermarket.

Should be totally safe to boil water in.