Why are our speedometer faces always brown?

[A383Wing]

Over the years I have noticed that almost every ralley cluster has a brown speedometer face, even when all the other gauges are a nice white color......I have 3 clusters here including the one in my car.....all the gauge faces have nice white lettering except the speedometer that's right in front of me.....

Can anyone tell me why this is? I have even seen this on low mile untouched original cars.....all the dash clusters look great, except the speedometer

Bryan

[birdsandbees]

Heat from the 5volt regulator.

[JB400]

Mine looks like it rusted, and it wasn't just the speedo on mine

[A383Wing]

Mine looksnlike it rusted, and it wasn't just the speedo on mine

Yea, that's what I'm talking about.....mainly I have seen this just on the speedo face

[BLK 68 R/T]

I read somewhere it was due to UV rays. The other gauges were in the right place to be out of the direct light. Can't remember where I read it though. Hell maybe I dreamt I read it