Is it possible to adjust selective colour from an area highlighted by the brush adjustment tool in Lightroom?
Additionally I can't see any options for luminance adjustment of brush adjustments either. How come that's not applicable here?
You can only do that globally in Lightroom. With adjustment brush you can only edit temperature, tint, exposure, contrast, highlights, shadows, clarity, saturation, sharpness, noise, moire, defridnge. Globally, you can adjust hue, saturation and luminance by dragging in the photo (similar to Photoshop) or by using sliders. For working with layers and masking use Photoshop.
When you select an area with the brush adjustment tool, you can modify the color of the selected area using the combination of Temp(erature) and Tint sliders, other than the whole selected area saturation with the related slider. You can also click on the "X" area next to 'Color' to open a panel for choosing color and saturation to use to fill the area.
Photoshop let you do more sophisticated adjustments. Luminance of the selected area can be changed with 'Exposure' slider as a whole, or with 'Hilight' and 'Shadows' if you want to work on those instead.