Regarding your last point, we only know that the flesh of a watermelon is indeed red because we've seen it before. If, say, an alien would suddenly come to Earth and be presented with a watermelon, they would not know what colour it is without cracking it open or otherwise probing it with various tools (granted of course that they perceive colour like we do)

Attributing nothing to the divine is also the way I go about it. We have scientific explanations for most phenomenon we see on a daily basis, and for those we do not, I do think we will find scientific explanations for them one day. None of the mysteries of the universe that would later be answered have been caused by the supernatural, so I have no reason to think it will be different.

However, I do think that a lack of observable trace of a "divine being" is not necessarily an evidence of nonexistence. To me, my agnosticism is not a form of compromise, but a recognition of the limitations of humans, as well as an acknowledgement relative inconsequence the question of whether a divine being exists or not is to the universe and to my own life. If nothing in my life or in the known universe can be attributed to the divine, why does it matter whether it exists or not? If an extraterrestrial exists in some distant galaxy, surely it would not matter to them whether I exist or not. That's the way I think of the idea of divine beings.

Anyways, it's kind of great to be able to ramble about this on the internet, most of the people I know are religious and unfortunately would not be very tolerant of this type of viewpoint.