Have I bought the wrong temperature sensor?

Hi everyone (yet again!)
I have ordered a temperature sensor from the lovely and very helpful Mike, of this parish, and duly fitted it. The thing that threw me, was the fact that the old sensor was black, not green! And the temp gauge is still taking a while to get up to 90. I didn't hit it in ten miles of mixed driving, this morning. To be fair, it was minus four! My mate thinks it could also be down to the fact that the engine undertray is missing. The thermostat was also changed. The engine carries the Avf moniker ;-)

Nice one, Paul. I thought you awesome lot on here would put my mind at rest. It does seem to run a bit smoother when it hits 90 - how long does it take for yours to get there? Thanks