Check out the documentation on Google Code on Themes for Chrome.
A theme is a special kind of extension that changes the way the browser looks. Themes are packaged like regular extensions, but they don't contain JavaScript or HTML code.
Basically, you create a manifest.json file, which contains all the data and information required for your theme (such as which images are used for which component of the GUI). Here's an example:
{
"version": "2.6",
"name": "camo theme",
"theme": {
"images" : {
"theme_frame" : "images/theme_frame_camo.png",
"theme_frame_overlay" : "images/theme_frame_stripe.png",
"theme_toolbar" : "images/theme_toolbar_camo.png",
"theme_ntp_background" : "images/theme_ntp_background_norepeat.png",
"theme_ntp_attribution" : "images/attribution.png"
},
"colors" : {
"frame" : [71, 105, 91],
"toolbar" : [207, 221, 192],
"ntp_text" : [20, 40, 0],
"ntp_link" : [36, 70, 0],
"ntp_section" : [207, 221, 192],
"button_background" : [255, 255, 255]
},
"tints" : {
"buttons" : [0.33, 0.5, 0.47]
},
"properties" : {
"ntp_background_alignment" : "bottom"
}
}
}
Once you have finished, packaging it up is just as simple as going to chrome://extensions in the address bar in Chrome, and click the Pack extension button. For more details, check out Packaging in the Chrome documentation