Regards that gap between the floor-end and the rear hull plate where the doors are...
It looks to me like the floor plate is simply a little bit short - its been years since I did one of these Dragon -251 kits, and I don't recall seeing such a gap - or maybe I just filled it or otherwise covered it up... Which is pretty much what I suggest is your "fix" for this: Just fill the gap with putty or a strip of styrene sheet and make the floor plate extend fully to the rear hull plate.
Regards paint colors... You have CHOICES and guide-lines...!
GENERALLY SPEAKING, German armor vehicles were primed in the well-discussed "Rot-oxid" or red-oxide primer, followed by factory painting in whatever the regulation base-coat color was AT THE TIME of manufacture. The choice of base-coat was purely by regulation - NOT by any seasonality.
So, IF your 'track was built between 1940 and Feb 1943, the typical regulation base-coat was the dark grey "Dunkelgrau". Starting in late Feb - early Mar of 1943, the regulation base-coat color changed to the mustard-brown color generally called "dunkelgelb" (dark yellow).
Regulations from July 1940 through Feb '43 prescribed that all vehicles would be a solid dunkelgrau. No official added camo color was regulation-prescribed for European theater / Russian theater vehicles - but many units and crews actually painted on camo colors obtained from various sources. From Feb, 1943, the reg base-coat was the mentioned dunkelgelb - and for most of the remaining 2 years of war, regs prescribed 2 general camo colors (a dark green and a dark red-brown) to be applied over the dunlekgelb - by units and / or crew in the field. The camo colors were provided from central stores and applied "at whim" by crew or at unit shops - hence the huge variation in camo schemes seen on German stuff in 1943 - '45. From Mar, 1943, older vehicles were repainted dunkelgelb and generally camo'd in brown, green, or both B abd G.
So... First determine whether you have / want a vehicle in service before Mar 1943 - IF SO, it will be all dunkelgrau (unless it is sent off to Africa - in which case it would be one of maybe 3 general "DAK - type" paint-schemes) exterior with MAYBE some added camo - which could be any of several colors (NONE of which were actually "regulation-prescribed" before 1943). IF a 1943 / '43+ vehicle, it will be base-coated in dunkelgelb, and may or may not be camo-painted over that (not every tank or 'track was actually camo-painted).
Note: There has been quite a bit of discussion on several sites regarding how to paint German open-top armor... In general, all the typically-visible interior should be the same color as the exterior base-coat. Folks vary about whether the driver's compartment would be painted in the typical German "elfinbein" off-white used in closed-top armor, and of course there are also discussions about the floor being maybe a different color (dark green, or...) then the interior hull-sides. I'm in the elfinbein driver's interior and dark green floor "school".
My suggestion is to spend a little while looking over -251 builds on the web, and / or reading some of these many threads discussing painting such builds over the years. Depending on your interests in "accuracy" versus build-appearance, form up your paint-scheme taking into acct whatever parts of those other builds and discussions you wish to consider. There is certainly the "right way", and any of many "good ways" to go! Of course, if you are REALLY MOTIVATED, there are many publications and oodles of web-discussions about these topics - but maybe you don't want to spend your life doing research over actually getting a build done! But its out there if you want it!
Cheers! Bob