There are measurands like humidity, where the green range is not on top nor on bottom, but in the middle. The yellow and red range are on both ends, see attached picture.
Feature request: Update the Gauge Card, that the severity can also be a range {min,max} or an array of ranges {min1,max1},{min2,max2}.
severity:
green: {35,60}
yellow: {20,35},{60,85}
red: {0,20},{85,100}
or similar, what ever notification you prefer 
Just noticed that you can get green in the middle as long as you are happy with one end yellow and the other red. if you set red to 0, green to 35 and yellow red on 60 this works.
you suggestion is better though but this might help in the meantime.
Personally I would also like more colors. Blue for temperature looks better but I am sure some applications might appreciate many more.
Agree, to allow additional color (specific blue for temperature) should be possible… and a pice of cake to program.
For the record if standard card is not enough for one, see custom:canvas-gauge-card
Ref : GitHub - custom-cards/canvas-gauge-card: The card makes it possible to use gauges from https://canvas-gauges.com/
It is however probably overkill for simple needs and the contribution of hansQ is perfectly fine (thanks!)