Hi. I'm not a pro so clearly may be wrong but I thought using dark floors, combined with very light walls and a white ceiling was actually a design trick for making ceilings look higher. Having such a contrast of the dark and light tricks the eyes into making the walls seem higher. I've attached a pic of my basement which is a lot lower than your ceilings (ignore my lighting over the bar table as this is meant to be a no no with low ceilings. Mine were just so low I went with what I wanted but it does show the contrast in floor!). Combine this with other design tricks ie wall lighting, low furniture, floor to ceiling curtains, hang pictures high, full height doors etc. if in doubt, do follow One Plans advice and see your space with different flooring options so you can decide rather than making a costly mistake

We have the same type of panelling in our hall and it was oak the same as yours with an oak floor. It just started to feel quite dark and drab but we hesitated to to do anything for fear of messing it up. In the end we painted all the panelling in Farrows French grey, left the doors and floors wood and painted the sides of our staircase and the spindles in Farrows clunch but left the newel posts and the bannister rail as wood - looks like a different hallway - I have never regretted painting it

I think you should stay within house style. Contemporary design may be too much. Color should match with your house facades and windows. Maybe something like this? Solid wooden door with glass in the middle. Graffiti grey color. Could be quite good match with any colours (specially with your bricks facade).

It sounds like the way you want this to improve your life, is to keep the home clear of dirty clothes and footwear - as having three boys can be messy! Your existing outhouse, is it insulated already? What is its size? Is it located along the journey into your home - i.e. can be visited by kids & adults to remove dirty clothes / wash hands / clean boots / change shoes - before going on into your home. If you have kids or family members that like messy arts, the room could also be suitable for that too? It's a question of size, location relative to the entrance to your house and whether the outhouse is or can be suitably insulated. If it solves your problems and makes life easier, then it could still be a luxury for you. Many people as listed in the comments above, tend to have the laundry facilities in dark, even damp places - this does not make for a pleasurable weekly chore. If your outhouse has windows, great, if not, consider adding more, using rooflights or at least use high quality daylight bulbs and add some appealing colour / decoration to the room. If the basic and regular activities of life can be lifted up toward a more enjoyable, rich and positive experience, then that is better for body and mind.