If it is natural stone, yes you can change the color. First step is removing any "sealer" (if present), then a thorough cleaning. Sometimes, a simple power-washing is enough, sometimes you need to scrub with TSP (rinse thoroughly). Observe all cautions re: TSP. You can apply a stain, or watered-down paint. Always experiment on a tile, buy a couple of new ones for that part. The difficult aspect is applying the new color to the whole project in one stage. Changes in humidity, or sunlight falling on the surface, can cause different absorption rates...and different colors. What you do on Tuesday may not match what you did on Monday. A "stone restoration" company might offer more tips. Remember, travertine is very porous, any "paint" will, in time, fade because of rain.

@chiflipper, Yes, it is natural stone. It is travertine. What would I do after removing the sealer? How would I be able to lighten or change the color?

Reread the entire comment.

" You can apply a stain, or watered-down paint."

Thank you! I apologize, for some reason I hadn’t seen the entire comment before. Thanks for your help.

Romabio has some limewash products meant for stone and brick to change the color.

I was thinking to do the same , also wondering how it all came out !!