Open the properties for "npc_portal_turret_floor" then click the "Edit" button so you're NOT doing a smart edit.
Then add property "rendercolor" and for the value put in the RGB value:

255 0 0 - Red
0 255 0 - Green
0 0 255 - Blue

Change the values from 0 to 255 for a combination that gives you the color you want.

Hi, I worked out my error a month ago and it works now, soI forgot to explain where I did my ♥♥♥♥ up
First the textures for turret_red.mdl
When I started to recolour the texture of the turret I forgot to do it in Gimp, so that I can add an alpha channel layer, the one resopnsible for the transparency of the image
Secondly, the vscripts, I used a vscript:
function ChangeModel()
{
Entities.FindByName(null,"modelname").SetModel("path/to/my/model.mdl")
}
This means that when you place the Turret entity in hammer you have to give it a name, like Suzie
Then you change the Entities.FindByName(null,"modelname") to Entities.FindByName(null,"Suzie") so all turrets named Suzie will be changed to the new turret model you've been working on