I painted my bedroom yellow. After 1st coat, its too dark of yellow. How can I lighten up the shade?
The best thing to do is buy more paint. Any changes you make will not be repeatable and paint is relatively inexpensive.
To answer your question, take a gallon of white paint and add small amounts of yellow to it.
OR……….. Go to a paint dealer and choose a color strength less than half of your first color and you will probably be happy. Yellows multiply in intensity.