I ran across this site while looking for other parts.  They do extruded color tubes in red and green in the correct 4 inch diameter.  The wall thickness is 1/8th inch.  For future builders

http://k-mac-plastics.net/acrylic-colored/colored_extruded_acrylic_tubes.htm#TRANSPARENT/TRANSLUCENT

Great find, Karst. But... you forgot to mention one little detail. For the 4-inch diameter tubes, the cost is $23.16 per foot, and the minimum order for the 4-inch tube is 24 feet - that's $555.84 for one tube. (That's one long tube, but you could build quite a few columns with it once you cut the lengths you need. )

I looked at the 7.5-inch diameter white (and frosted) tube for the late Hartnell-early Tom Baker TARDIS lamp. The minimum order for that one is 6 feet at $64.42 per foot. That's $386.52... too deep for my wallet. (I think I'll just keep on my son's back until he 3D prints the frosted cylinder he's promised me. It might take another 6 months, but it's still free!)

Dino.

There a many sources of cheaper tubes. The actual prop used clear ones with color gels inside. I'm using colored ones for my 1:4 for convenience, though.

In the US, Tap Plastics used to be a great place for things like this. Unfortunately they've re-arranged things on their site, and changed their offerings. Now the largest diameter colored tube you can get is 2 inches outside diameter (OD) with a 1/8th-inch thick wall.

They do still sell the clear tubes at 4 inches OD (and larger ones) with 1/8th-inch thick walls. They all come in 6-foot lengths, and for the 4-inch OD tube it's $96.40. However with that, like lespaceplie says, you'd need to use colored gels inside the tubes, like the BBC did on the original to get the color you want.

Still, $96.40 is a heck of a lot less expensive than the $555.84 K-mac Plastics is asking, and you don't have to order a minimum of 24 feet. With Tap Plastics, each tube is standard 6 feet long, which should give you three tubes for the central column, with a little leftovers if the tubes inside it aren't a full 2 feet long.

Dino.