Christmas lights come in two main varieties: flashing lights and nonflashing lights. Both varieties can be white, red, blue or coloured. If you want your flashing Christmas lights to stop flashing, you can do it by using replacement bulbs. Only certain lights on a flashing light strand cause the other lights to flash. If you take those out and replace them with standard lights, the lights will stop flashing.
Unplug the Christmas lights from the outlet.
Go over the lights one by and one and locate all of the lights that generate the flashing and remove them. They are usually clear with a red tip.
Replace the flashing lights with a standard light of the colour of your choice. Make sure you've replaced all of the lights that cause the flashing on the strand.
Plug the Christmas lights back into an outlet. They should no longer flash.