Different 'Brush modes' help in quickly selecting (and de-selecting) features in the image.
For example, while in 'Flood fill lighter pixels' mode, try clicking next to a bright star or feature to select it. Click anywhere on a clump of 'on' (green) pixels, to toggle the whole clump off again.
The mask editor has 10 'Brush modes';
The 'New Darker Than Old' parameter sets whether newly created pixels should always be darker than the old pixels.
The Heal module was created to provide a means of substituting unwanted pixels in an neutral way.
Thanks to StarTools' Tracking feature the Color module provides you with unparalleled flexibility when it comes to colour presentation in your image.
You can convert everything you see to a format you find convenient. Give it a try!