I am not the right person to answer this because I am the quite opposite of you, I have a knack for design, but still learning how to code a skin properly.
With design you just kinda have to know what people like and what people don't like. There is really no wrong way to design (That is saying what your audience is going to be like and to be honest I think
most designs are nice, it's the colors that are a problem that makes designs look horrid). Your design can be good, but the colors you choose makes a whole lot of difference.
Someone can have a nice design, but it can be ruined with the colors. But that isn't what you really are asking haha. Anyways, when I think of design for posting templates at least or even skins (even though I can't code) I bring up paper and jot down what I want or even sketch what I'm imaging. There are times where I will open up photoshop / paint and mess around with shapes organizing what goes where and how it should look.
For me paint is easier with posting/plotting templates because it lets me see visually how many boxes in the table I need or what margins I need to use.
Again I never coded a skin on a proboards at least since pbv5 has been out so my advice probably isn't as helpful as a skinner who has coded in pbv5. For inspiration I will look at other people's designs and see what people like and what people don't like and put my own twist to it.
For colors, again, it is what your audience is like. I learned that people like darker themes, but I myself prefer lighter themes. Just depends on who you are asking.
I prefer themes that have neutral colors so to speak: browns/greys/blacks/white with a dash of secondary/primary colors.
Like for example, GS. (sorry I won't use gs for an example if you don't like it) The main color is grey and there is pink here and there. It isn't the main color, but it is noticeable to where people will notice this is a pink theme. The pink is still a bit bright, on my computer at least, but it is a nice pink overall. It makes the theme flow evenly.
Another example would be
RESET (owned by
middy♥) which
PHARAOH LEAP coded. It has a simple, but compact design. Not all compact designs are bad. I say compact because the banner is a hover, but it's still simple and easy on the eyes. The colors used throughout the theme is from the banner / image. But the red / green on the image are used for the subtle areas (recent posts, cbox rules, links)
here are some other sites I think have a great design:
here by
DARKEE,
here by
beekeeper ... I had more to post, but they all seem to put in Maintenance Mode. haha guess that's it for now.
Again it just depends on the skinner and what they think people will like and what the skinner likes! For what I suggest though is just open photoshop and mess with shapes because that is what I do while getting inspiration from other theme makers or even designs themselves like in magazines, or articles. Even music can help inspire you.
Some people start with the banner and others plan out while they code. I think you just have to find what suits you. I kinda didn't answer your question so I hope someone better
that I tagged can answer your questions! good luck! ouo /
I forgot to say, try to know your limits in your design. Some people have this great design and then they try to code it, but cannot because they do not know how. Know your limits on what you can code and what you cannot code because it will be easier on you and less frustrating. Simple is not bad. Simple is a start. Simple is still a design. It's best to know your limits in both design and coding.
hopefully i didn't offend anyone saying all this haha. And while we aren't talking the difference between art and design, I still think this falls under what you are asking
good design is an opinion.