What do the different colored bars in the query editor menu mean in SSMS?

Question

What's the significance of the color change in this picture?

EDIT: I was referring to the yellow and green areas of the scroll bar.

Answer 1

Blue  - SQL keywords - query specification components
Pink  - Functions
Grey  - SQL predicates
Black - table/column names/aliases

The colored bars on the left, next to the line numbers, appear next to lines that have been changed since opening the file:

Yellow - Changed lines that have not been saved
Green  - Changed lines have already been saved