All colors of PEX pipe are made the same and can be used for both hot and cold water.
But the main difference between the red and blue colored PEX pipe is that the blue PEX pipe is made for and is color coded to mean that cold water is flowing through the pipe while the red PEX pipe is used for hot water and means that hot water is running through that line.
So when PEX pipe is installed the installer or plumber will use red PEX pipe for hot water lines and the plumber or installer will install blue PEX pipe for cold water lines.
So that's the only difference in the red and blue PEX is the temperature of the water flowing through it.
You can use either color of PEX for hot or cold water but it's best to run red PEX for hot water and blue PEX for cold water to be able to identify the pipes going to which faucets and lines so it makes it easier to repair if you need too.