My 69 has a temp gauge in it that appears to be from a later model.  It has a max temp of 280 degrees and the numbers are white.  My other gauges have green numerals which I believe is correct.  Qusetions are:

The gauges on a '69 should indeed be green numbered.

To replace the gauge, you need to remove the cluster assembly...not an easy task at times, due to the thinness of the gauge panel just above the gauges. They will break there if not handled carefully.
You could replace the sending unit with one for a later car, but that may not completely give you a correct temp reading, either.

If you have a service manual for your car, follow the instructions on removal of the gauge panel/cluster. If not, you probably will need to remove the shifter console first, and then the screws holding the gauge cluster to the dash panels, and to the top dash pad. Look carefully, as there are a couple of screws that can be missed.
Once you have the cluster loose, carefully pull it out, making sure you don't pull any connectors loose that you can't identify later. Photos are a big help!
Mark/tag everything!

When you have the cluster out far enough to get the rear of the gauge "cover" off, remove that, and then the gauge.

If you take your time, and work carefully, this shouldn't be too big of a job. The factory service manual is highly recommended.

Perhaps someone else with a '69-'69 will have more removal info.

as joel said be careful of the panel when removing. take either shifter cover off or side access panels off as there are two nuts holding it in. if original radio is in take off knobs and nuts hold stems in place. on my 75 there are about eight screws to remove. 4 on the side, 2 under side of dash in front of wiper switch and two front under wiper switch. gently pull and should come out to be able to take off wire connections. there are about four small nuts holding cover on and should be able to get the rest off easily. just have to rember how it goes back. when i got my 75 and took it out it came out in two pieces. thought thats how it was suppoed to be but found out it is all one piece except for the wiper switch. check out ebay motors as i have seen a lot of guages there at times. good luck.

Both Joel and David are leading you down the right path. As Joel suggested a service manual would be very helpful to you. It just so happens I saw this one on EBAY earlier and thought you might be interested. Good Luck...
                                      
                           Tux...   


MANUAL LINK

Dang!! That's CHEAP!! Someone oughta grab them quick! Reserve of $12? Can't go wrong if the set gets up to $50-$60,imo.

Thanks for the tips guys.  I have several service manuals including the Assembly Manual.  I'll try and give it a shot this weekend.

I would also recommend blocking the tires and moving the shifter into 2nd or 4th, the farthest away from the cluster.  Otherwise, you stand a good chance of knocking it out of gear and could roll into somewhere you didn't anticipate.

i find that removing the dash from the passenger side is very easy and makes it much easier to get to the center cluster..