I appreciate all feedback and don't consider it a complaint if somebody has a suggestion. Because of the variety of settings, I don't personally see all the possible configurations, so I may not be seeing a problem that is obvious to you.

You can create a background color theme by using the options to set color levels and texture. If you use a custom background image you may want to set the scroll/fixed setting to one of the "fixed" options. The fixed/cover and fixed/stretch options will both fit the image to the window ("cover" will maintain image aspect ratio, "stretch" will match window's aspect ratio).

The "main sections color" setting will set the color of a highlighted section on the main pages (like search results on the search results page or the main feed on the home page.) If you don't want it you can choose "0% (invisible)" for the main-sections-opacity setting.

If you want to edit things like link colors, or if you want to use the no-option version of the style (to get auto updates) and customize the options, without needing to re-edit after each update, use http://freestyler.ws/style/75119/override-youtube-styles.

I use the https://userscripts.org/scripts/show/114002 userscript which allows centering of the watch page and player as well as many other useful functions.

My custom scrollbars are based on userstyles's userstyles's Eli (Ukiss) & Sungyeol (Infinite) by makondo@userstyles.

2014-07-07: removed white background in new account pop-up
2014-06-12: removed white borders on player description area
2014-06-05: fixed gray player "theater background"
2014-04-24: fixed white background for video names and descriptions
2014-03-04: added option for non-scrolling top bar (which is YouTube's normal behavior now)
2014-02-28: fixes for "youtube mix" right sidebar, misc
2014-02-21,22: fixes for new layout
2014-02-16: modified so Google+ comments are only affected on YouTube site
2014-01-29: fix watch page icons
2014-01-28: fix expanded menu
2013-12-06: additional comment section improvements from TokHaar@userstyles, fix tags pages
2013-12-05: improved watch-page playlist appearance
2013-11-19: fixed homepage/subscription-feed-page problem seeing/accessing guide and recommended channels, fixed some stuff in video editing pages
2013-11-07: fixed new comment section (I hope)
2013-08-29: centering option off by default
2013-05-01: fixed player-width bug (centering enabled) and showed One-Channel channel banner (channel background enabled)
2013-03-17: I changed the Firefox scrollbars - in Windows they look better, but I don't know if they work in Mac or Linux
2013-03-13: Update for YouTube watch page changes
2013-03-13: Fixed video comments voting icons, added improved Firefox scrollbars.
2013-03-13: Fixed centering problem - thanks to SOCOM-HERO for notifying me.
2013-03-01: Changed image hosts for icons - may be some malfunctions until I find out what limits are. I'd appreciate info on what host(s) will host .pngs and provide substantial bandwidth (10 Gb/mo +) for free.
2013-02-04: added main-section-opacity setting, revamped expand-sidebar option so it works with small player, added background-visibility settings for greater/complete visibility, added compatibility with Resize YouTube Player to Window Size script, expanded playlist tray video title to 2 lines.
2013-02-04: fixed inability to click on guide on watch page
2013-02-01: tweaks including video manager and channel settings pages
2013-01-31: misc fixes including centering and white backgrounds, and your own channel and playlists with "show channel background"
2013-01-23: minor fixes and improvements, added background image options fixed/cover, fixed/stretch, fixed/tile, fix for footer update
2013-01-18: fixed centering in Chrome
2013-01-17: improved channel background option, improved default scrollbars for Chrome (but why would anyone not use my dark scrollbars???), fixed white footer in Chrome, misc minor tweaks (thanks to deevious for feedback)
2013-01-16: added channel background option, improved compatibility with YouTube Better Start Page and YouTube Center, misc tweaks
2013-01-07: provided centering option based on http://freestyler.ws/style/73975/youtube-s-new-layout-centered-updated-may-08-2014 by arcadesdude@userstyles. Also provided option to widen sidebar on watch page (if space is available), which only works if you also choose "Yes" to the "center page and player" option. Styled YousableTubeFix config dialog.
2013-01-04: autohide feedback button, misc tweaks
2013-01-02: design changes - let me know of problems. The new look is a little different, let me know if you like it.
2012-12-27: styled YouTube Center config panel, other minor things
2012-12-22: fixed "all comments" page, enhanced scrollbars, misc
2012-12-18: made doodle logo visible with working links
2012-12-17: misc minor improvements, including fixing a glitch on the home page feed
2012-12-13: removed link colors (to revert or customize them, see my new http://freestyler.ws/style/75119/override-youtube-styles). Visited links dim on hover, un-visited brighten
2012-12-06,08: ***updated for the new layout***