When I see a black pixel only on a blue screen, is that a stuck pixel or dead pixel?

Solution 1:

Dead.

Stuck is ON, dead is OFF.

Pixels are created from sub-pixels of primary colors, typically red, green, and blue:

The reason the dead spot is visible only when blue is displayed is because it is a blue sub-pixel that is dead. When the background is blue, that is the only color on, and it stands out. When the background is another color, the other sub-pixels reproduce it or it is still bright and absent blue, which is less noticeable.

For example, you can see yellow because it is created from red plus green. A white pixel with a dead blue sub-pixel will produce yellow, which isn't very noticeable in a bright spot that small.

There is a guide at digitaltrends.com for various methods of attempting DIY fixes for stuck or dead pixels - though it must be noted that it's
a) very hit & miss &
b) potentially damaging to the rest of your screen if attempted too enthusiastically.