I have a suggestion/bug report. It seems that Screenshot Captor currently does not support colour management. Basically it captures the colour values as sent to the monitor and stores them in a file with sRGB as colour space. However, if the monitor uses another colour space (ICC profile), as is typically the case for wide gamut monitors and monitors calibrated/profiled, then the colours recorded by Screenshot Captor are in that colour space and will be wrongly interpreted as sRGB. Typically that leads to washed-out/less-saturated colours.
If you have Photoshop or a similar tool, there is a workaround for that. First assign
(NOT convert to) the monitor colour space to the image, then convert
it to sRGB, or another working colour space such as ProPhoto RGB. But of course it would be nicer if Screenshot Captor would do that automatically.