First, consult this thread... https://forums.galciv2.com/170646
Secondly;
Do I have to tweak something other than the gfx files,
Yes -- possibly Surface Raws, certainly TerrainColorSchemes.xml(TCS) & PlanetDescriptions.xml(PD) files.
Oh, I did that- Changed the RAWterrain tag to PlanetOceanic_1.raw from the hightsmap file, and also changed the terrain pallete tag to "Oceanplanets1" as seen in Planetary Descriptions. That's why I asked whether that was the problem, and I should have left it as earthlike or "testing123" or whatever. If I just leave terrain palette tag out? It seems to work for other custom planets. Or should I perhaps copy and rename the .raw file from "PlanetOceanic_1" to my homeworld's custom name?
EDIT: So I took out the "Aquatic" tag, and used the earthlike planet description for terrain palette. The game still crashes. Apparently the problem's with the homeworld RawTerrain and TerrainPalette tags, since they're essentially the only ones I change (besides giving new names for the star and planets).
or do all homeworlds have to be earthlike?
Sadly alllllmost yes... but i refuse to submit to this incode obstacle created by SD, if anything i'd break the PQ sequencing limits applied to HW (10), secondary planet (4) and all the rest at Zero. As such, indirectly, it is possible to mod some of the Earthlike 'context' and use alternate text & graphics to change them (Scanning properly for Queries between planets & matching description with the real text strings isn't fixed yet, but that's a different issue). The term CustomPlanets has to mean something or at least be much more controllable than it already is. In fact, once they make their own map Editor truly compatible with the CP file (of both DA & TA, btw), then i'll consider adding more diversity to surfaces.
If so, can the planet at least look like an aquatic one?
Yes. The OceanLike TCS is indeed a tricky set of colors for such surfaces.
But what do I have to do to even make it look aquatic superficially? The terrain control scheme is determined by your choice of planetary description for the TerrainPallette tag, right? Or have I got this all wrong?
Sorry if I'm missing something obvious- I don't have much experience with this, since any general tweaking with games I've done until now was restricted to old SE4 shipsets and races. There's great potential in ToA that I've been missing, and perhaps I'm diving in too fast.