an easy option for you is to
choose the muddy type texture or stone texture then change the fog, ambience and surface colours.
this should for now help
unless you know about normal diffuse and speculars with alpha channels
then you get your desired texture save as diffuse
then do a specular ie a black and white texture ( this helps to make things more shiny if they are whiter) then add an alpha channel and apply alpha mask.
then make a normal map using gimp or other art package that has a texture transformer. than save as is and copy the other files change to assign to your texures and you should be good to go i am to be honest very limited with reloaded as i am modelling stuff for it at the moment as the engine is not at the creative level i can work with just yet so rather than wait about i am making monsters and dungeony stuff etc.
also read the manual in the doc folder in the main program files of reloaded , this is where you can tinker and look at how it all works. i am as i say not very versed in ground editing yet. or even lua scripting. but i do know for now they give you sky box. no dome.
and it wont come anytime soon, we dont even have water yet or basic core functionality which is what they are working on. we must be patient and find work arounds.
there are sky box makers out there search tgc forums there are links
hope this helps keep happy
an unquenchable thirst for knowledge of game creation!!!