These are reflecting my personal minimums and maximums, but are done according to the POH and usual practice.
For example the CHT can be above 200C, but it's common to be careful to avoid it. Thus the yellow. Also the yellow band in RPM and MP is according to the indications in the POH in terms of cruise settings.
In general I prefer yellow bands to black (or lack of bands) when outside the green or operating areas. For example the huge range above the operating area of oil pressure, or the part below in CHT. It's easier to visually notice that something is wrong if it's yellow, even if it could perfectly operate there. Early warning, is my thinking. Also, colors gives life to the instruments, so it's looking good too.
