The results of what follows are very close to the look of solarized but not perfect. Basically, I used this this stylesheet for solarize and went through selector by selector and did my best to translate it into the styles used by Coderay.
Here is the original solarized example for ruby:

Here is the results I am able to produce with coderay:

SO: it's not perfect, but will get anyone that wants to use a Solarized-like 'theme' for Coderay on their way.
Here is what you need to do (for a Rails 3 app):
First you will need to override the module within the coderay gem that it uses to generate inline styles. Create a file called coderay.rb
within config/initializers
.
Next paste in the following into the config/intializers/coderay.rb
file you've just created:
module CodeRay
module Styles
# A colorful theme using CSS 3 colors (with alpha channel).
class Alpha < Style
register_for :alpha
code_background = '#073642'
numbers_background = 'hsl(180,65%,90%)'
border_color = '#c0c0c0'
normal_color = '#d5f6f6'
CSS_MAIN_STYLES = <<-MAIN # :nodoc:
.CodeRay {
background-color:##073642;
border:1px solid #c0c0c0;
background: #002B36;
color:#eee8d5;
}
.CodeRay pre {
margin: 0px;
}
span.CodeRay { white-space: pre; border: 0px; padding: 2px; }
table.CodeRay { border-collapse: collapse; width: 100%; padding: 2px; }
table.CodeRay td { padding: 2px 4px; vertical-align: top; }
.CodeRay .line-numbers {
background-color:#d5f6f6;
color:#808080;
text-align:right;
-webkit-user-select:none;
-moz-user-select:none;
user-select:none;
}
.CodeRay .line-numbers a {
background-color:#d5f6f6;
color:#808080;
text-decoration:none
}
.CodeRay .line-numbers a:target { color:#00f !important; }
.CodeRay .line-numbers .highlighted { color: red !important; }
.CodeRay .line-numbers .highlighted a { color: red !important; }
.CodeRay span.line-numbers { padding: 0px 4px; }
.CodeRay .line { display: block; float: left; width: 100%; }
.CodeRay .code { width: 100%; }
MAIN
TOKEN_COLORS = <<-'TOKENS'
.debug{color:#fff;background:#00f}
.annotation{color:#586E75}
.attribute-name{color:#93A1A1}
.attribute-value{color:#93A1A1}
.binary{color:#509}
.char .content{color:#d20}
.char .delimiter{color:#710}
.char{color:#2AA198}
.class{color:#268BD2;font-weight:bold}
.class-variable{color:#268BD2}
.color{color:#eee8d5}
.comment{color:#586E75}
.comment .char{color:#859900}
.comment .delimiter{color:#859900}
.complex{color:#a08}
.constant{color:#B58900;font-weight:bold}
.decorator{color:#268BD2}
.definition{color:#099;font-weight:bold}
.delimiter{color:#000}
.directive{color:#088;font-weight:bold}
.doc{color:#93A1A1}
.doc-string{color:#93A1A1;font-weight:bold}
.doctype{color:#DC322F}
.entity{color:#CB4B16;font-weight:bold}
.error{color:#93A1A1;background-color:#faa}
.escape{color:#CB4B16}
.exception{color:#CB4B16;font-weight:bold}
.float{color:#2AA198}
.function{color:#268BD2;font-weight:bold}
.global-variable{color:#268BD2}
.hex{color:#2AA198}
.imaginary{color:#f00}
.include{color:#b44;font-weight:bold}
.inline{background-color:transparent;color:#93A1A1!important}
.inline-delimiter{font-weight:bold;color:#DC322F}
.instance-variable{color:#268BD2}
.integer{color:#2AA198}
.key .char{color:#DC322F}
.key .delimiter{color:#268BD2}
.key{color:#859900}
.keyword{color:#859900;font-weight:bold}
.label{color:#93A1A1;font-weight:bold}
.local-variable{color:#268BD2}
.namespace{color:#859900;font-weight:bold}
.octal{color:#2AA198}
.operator, .predefined{color:#859900;font-weight:bold}
.predefined-constant{color:#2AA198}
.predefined-type{color:#DC322F;font-weight:bold}
.preprocessor{color:#859900}
.pseudo-class{color:#859900;font-weight:bold}
.regexp .content{color:#2AA198}
.regexp .delimiter{color:#DC322F}
.regexp .modifier{color:#CB4B16}
.regexp{background-color:transparent}
.reserved{color:#268BD2;font-weight:bold}
.shell .content{color:#2b2}
.shell .delimiter{color:#161}
.shell{background-color:transparent}
.string .char{color:#2AA198}
.string .content{color:#2AA198}
.string .delimiter{color:#DC322F}
.string .modifier{color:#2AA198}
.string{background-color:transparent}
.symbol .content{color:#2AA198}
.symbol .delimiter{color:#2AA198}
.symbol{color:#2AA198}
.tag{color: #268BD2}
.type{color:#DC322F;font-weight:bold}
.value{color:#268BD2}
.variable{color:#268BD2}
.insert{background:transparent}
.delete{background:transparent}
.change{color:#CB4B16;background:transparent}
.head{color:#CB4B16;background:transparent}
.head .filename{color:#CB4B16}
.delete .eyecatcher{background-color:rgba(255,0,0,0.2);border:1px solid rgba(230,0,0,0.5);margin:-1px;border-bottom:none;border-top-left-radius:5px;border-top-right-radius:5px}
.insert .eyecatcher{background-color:rgba(0,255,0,0.2);border:1px solid rgba(0,128,0,0.5);margin:-1px;border-top:none;border-bottom-left-radius:5px;border-bottom-right-radius:5px}
.insert .insert{color:#CB4B16;background:transparent;font-weight:bold}
.delete .delete{color:##2AA198;background:transparent;font-weight:bold}
.change .change{color:#CB4B16}
.head .head{color:#CB4B16}
TOKENS
end
end
end
You'll also add the following CSS to your application (or, if you want, make a file in assets/stylesheets
called coderay.css
for it):
pre {
background: #002A35!important;
color: #93A1A1!important;
}
The above will set your code background to the dark background used by solarize and any code not annotated by codeway to the fallback color used in solarize.
Now just restart your app.
** Again, this isn't perfect and youll probably want to crack open that coderay.rb
file again at some point and refine things. You can use this to help with that: http://jsfiddle.net/bradleygriffith/CNTw4/ **