to CHANGE the color of your hair. Just like you would if you go OUTSIDE and tan. HAIR COLOR will CHANGE with the sun. The darker color that you are experiencing is starting to bring out the RED in your hair. Any lightening...(depending on the person some people NEVER go into reds) However, lots of people the FIRST
color that they go through when lightening the hair is RED...or GOLDEN RED colors. You may be experiencing this color change....just like you would out in the real sun.