Man pages matching name qwtlinearcolormap in section 3:

QwtLinearColorMap.3.en	debian 10 / libqwt-doc
QwtLinearColorMap.3.en	debian 10 / libqwt5-doc
QwtLinearColorMap.3.en	debian 11 / libqwt-doc
QwtLinearColorMap.3.en	debian 12 / libqwt-doc