Fill rows and columns

Every row and column should contain as many reds as blues. If half of the spots are filled with blue then the remaining spots must be red.

Find numbers that can not be certain color

Number tells you how many surrounding spots are of that color. Since there are three blue spots around the empty spot with number two, the empty spot can not be blue, therefore it must be red.

Red with the number two must have two red spots around it. There is only one red around it, so the only remaining empty spot must be red.

Curious case of number four

There are eight surrounding spots around number four. Surrounding spots have four reds and four blues regardless of its color. If the highlighted spot would be red, remaining spots would be blue, resulting in an error. Therefore the highlighted spot must be blue.

Running into errors

Filling either of the highlighted spots with blue would result in an error with the spot numbered with zero. A zero must have zero spots of that color around it. Therefore both of the highlighted spots must be red.