#1
I have a table with black lines, black text and a white then blue then white... backing color and I want to change the blue in the table from which is covered in text to all white.

so how do I tell photoshop to select all the blue color while leaving all the other colors alone?

I have to select the white in between the letters on the table too.
#2
Look for the colour selection tool.

It should look like three coloured squares with a cursor on it.

You can change the threshold level too, in case it doesn't pick out all the blue.
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