What should I do

[MR.Amsterdam365]

The tips are changing colors

 

[DCLXVI]

Nute burn? try backing off the feed a bit? Hard to know what's up without just a bit more information.

 

[LabRat]

Almost every strain I've grown in the last 20 years does that so not to worry. If the edges of the leaves begin to look more jagged and their pointy tips begin to brown then you have nute burn starting for sure. Most plants go very dark green before burn starts and yours don't look all that dark. Overfeeding regularly eventually leads to toxic salts buildup that shows up in mid-flower and can't be fixed.