Appearance of the forum has a key role in attacting users. Most of the forum softwares available today has theming support.
Default forum theme may not be that much appealing to users. If you know the some design basics, you can chose any of the free themes available and add your customizations to it.
Many companies are working on forum themes development. Buying one of them also a good idea. One positive part of such premium themes is they will have a lot of customization options available(without coding) through which you can make your forum unique. Both in terms of color scheme and layout.
How did you choose theme for your forum? Are you using free theme or premium theme for your forum?
I’m utilizing a free theme on my site and now used a premium as you suggested on my forum to work well with the CMS platform that I used but not all premium themes have customizations options and I still edit the css of the site.