Plant Pot Trays Why Is The Bottom Part Of My Clay Planter (flower Pot) Discolored?

Why is the bottom part of my clay planter (flower pot) discolored? - plant pot trays

I have a potted plant, which is located in one of those typical clay pots, which can be purchased anywhere. Anyway, the bottom inch or less in the pot a strange color. I water my plant (once per week, the recommended amount for this type of investment is) and has a tray that excess water flows. What's wrong? "I am I very confused about the plants and therefore appreciate any comments. Thanks!