Customized copy of SpaceCadet.tmTheme, aka SpaceCade.solarce.tmTheme. I use it with sublimetext2. Included a custom color for "string source.ruby.embedded.source" which is what matches interpolated strings in Ruby code

SpaceCadet.solarce.tmTheme

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>author</key>
	<string>Alex Ross</string>
	<key>comment</key>
	<string>Created by Alex Ross</string>
	<key>name</key>
	<string>SpaceCadet</string>
	<key>settings</key>
	<array>
		<dict>
			<key>settings</key>
			<dict>
				<key>background</key>
				<string>#0D0D0D</string>
				<key>caret</key>
				<string>#7F005D</string>
				<key>foreground</key>
				<string>#DDE6CF</string>
				<key>invisibles</key>
				<string>#BFBFBF</string>
				<key>lineHighlight</key>
				<string>#00000012</string>
				<key>selection</key>
				<string>#40002F</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Comment</string>
			<key>scope</key>
			<string>comment</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#AE81FF</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>String</string>
			<key>scope</key>
			<string>string</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#CF7D34</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Constant</string>
			<key>scope</key>
			<string>constant</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#A8885A</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Variable</string>
			<key>scope</key>
			<string>variable.parameter, variable.other</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#596380</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Keyword</string>
			<key>scope</key>
			<string>keyword - keyword.operator, keyword.operator.logical</string>
			<key>settings</key>
			<dict>
				<key>fontStyle</key>
				<string>bold</string>
				<key>foreground</key>
				<string>#8F9D6A</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Storage</string>
			<key>scope</key>
			<string>storage</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#9EBF60</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Entity</string>
			<key>scope</key>
			<string>entity</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#6078BF</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Inherited class</string>
			<key>scope</key>
			<string>entity.other.inherited-class</string>
			<key>settings</key>
			<dict>
				<key>fontStyle</key>
				<string>italic</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Support</string>
			<key>scope</key>
			<string>support</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#8A4B66</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Exception</string>
			<key>scope</key>
			<string>support.type.exception</string>
			<key>settings</key>
			<dict>
				<key>foreground</key>
				<string>#893062</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>Tag name</string>
			<key>scope</key>
			<string>entity.name.tag</string>
			<key>settings</key>
			<dict/>
		</dict>
		<dict>
			<key>name</key>
			<string>Tag attribute</string>
			<key>scope</key>
			<string>entity.other.attribute-name</string>
			<key>settings</key>
			<dict/>
		</dict>
		<dict>
			<key>name</key>
			<string>Library constant</string>
			<key>scope</key>
			<string>support.constant</string>
			<key>settings</key>
			<dict/>
		</dict>
		<dict>
			<key>name</key>
			<string>Library class/type</string>
			<key>scope</key>
			<string>support.type, support.class</string>
			<key>settings</key>
			<dict/>
		</dict>
		<dict>
			<key>name</key>
			<string>Library variable</string>
			<key>scope</key>
			<string>support.other.variable</string>
			<key>settings</key>
			<dict/>
		</dict>
		<dict>
			<key>name</key>
			<string>Invalid</string>
			<key>scope</key>
			<string>invalid</string>
			<key>settings</key>
			<dict>
				<key>background</key>
				<string>#5F0047</string>
			</dict>
		</dict>
		<dict>
			<key>name</key>
			<string>- Meta</string>
			<key>settings</key>
			<dict/>
		</dict>
		<dict>
			<key>name</key>
			<string>  function.section</string>
			<key>scope</key>
			<string>meta.function.section</string>
			<key>settings</key>
			<dict>
				<key>background</key>
				<string>#371D28</string>
			</dict>
		</dict>
		<dict>
		    <key>name</key>
		    <string>Embedded Ruby Source</string>
		    <key>scope</key>
		    <string>string source.ruby.embedded.source</string>
		    <key>settings</key>
		    <dict>
		        <key>foreground</key>
		        <string>#2E6FD9</string>
		    </dict>
		</dict>
	</array>
	<key>uuid</key>
	<string>2C24E84F-F9FE-4C2E-92D2-F52198BA7E41</string>
</dict>
</plist>

Here is what it looks like with Ruby code: