I agree with some of your poitns, and I disagree with some of your points. I think your point about needing a floor to be comfortable is cogent however. I'll change my ruling on floors now.
Below is my take on the matters of adjudication in this spell:
1) It seems we're in agreement on the volumetric hemisphere with the plane of symmetry as "force floor/substrate." Thus the following logical inference here from (a) the 3D geometry and (b) the fact that the internal climate is regulated. It just says "it's dry and comfortable." Anything beyond that (such as a magic space heater) is beyond inference or extrapolation. Here is what I think is easily inferred. A shaped (be it hemisphere, sphere, or cube) "forcefield" in D&D prevents:
- physical travel (so no precipitation nor groundwater nor meltwater...hence "dry").
- Ethereal travel
- Conductive heat transfer. So the space neither loses nor gains heat from the outside, hence perpetually "comfortable."
The evidence is significant (legacy, logical inference, and Lead Designer).
2) The book is silent on the procedure of coloration blending in with natural surroundings. One can either assume (a) color is merely "color" or (b) it is an actual input to action resolution (which is what it has been historically). So, with (b) we have to determine a procedure for action resolution. Arcana vs Perception (with all the other dynamics I canvassed above - Adv/Disadv, Survival either to Help or as primary camo).
3) Ethereal travel is prevented. Legacy + other Force effects + DMG explicitly and clearly (in a rare 5e moment!) stating it.
So I'm assuming you disagree with 2? Do you think being able to color it is not an input to action resolution or do you think my procedure is off?