How tall is the Monument?

555 feet 5 and 1/8 inch tall.

How much does it weigh?

Estimated at 80,000 tons

Why does the color change on the outside of the monument?

When the monument was under construction the project ran out of money.  It sat uncompleted for 27 years until they could restart the project the stone above the line wasn't exposed to 27 years of pollution and wind driving dirt/dust.