Hey guys I am trying to change the Light bar color from Red/Blue to Blue/Blue. Does anyone know how? 

The light bar I am using is the one below, I would like to chose a different one if possibly if someone can help! 

Check the texture file should be police.ytd or whichever vehicle you replaced/added followed by .ytd. If you open the .ytd file using openIV you should be able to export the texture for the lightbar, modify it using GIMP or some other texture editing program then replace it using OpenIV's edit mode. You should be able to find a good tutorial online that goes into more detail. Also you will probably need to change the actual light emissive texture too, which should be in the same file. Look for a random looking texture of red and blue shapes that kind of match what the light pattern is, usually red and blue squares on a black or clear background. I attached an example of the emissive texture file for one of my vehicles.

Kind of like this? It was Red/Blue before now its Blue/Blue but I can still see Red coming from them. How would I add just a blue Light bar? also add more lights? If someone can make a good tutorial that would be great! 

Yeah, like that. The lightbar glass color like in your original picture should have its own texture file that will look similar to the lightbar in shape and color. Changing that should alter the glass for when the lights aren't activated. As far as the red you are seeing it may be the in game corona effect from the lights. I am not sure how to correct that but I believe the carvariations file may have something to do with it. Hopefully someone with a little more car modding experience can help further. I used the Ford Police Utility Interceptor with the same lightbar you have pictured. When I replaced the default texture in the .ytd file using OpenIV it changed the lights so that they were all red and blue instead of the default yellow on the rear of the lightbar. As far as adding more lights that is a vehicle model issue and I don't have any experience in creating car models.

Good luck!

There is a mod i downloaded which made it to where u could choose the colors ur lights emit...better emergency lighting is what it's called i believe easy install as well