How can I automate the "use dark menu bar and dock" preference in Yosemite?

I love the dark menu bar and dock feature in OSX Yosemite! However, I think it would be perfect if I could change it without having to open System Preferences every time. I have absolutely no experience whatsoever with AppleScript, but I'm trying to figure out how to write an AppleScript that will set the dark setting to on or off. I found this example on macosxautomation.com:

tell application "System Events"

tell appearance preferences

get properties

--> returns: {scroll arrow placement:together, font smoothing limit:4, recent applications limit:10, scroll bar action:jump to next page, double click minimizes:true, recent servers limit:10, appearance:blue, recent documents limit:10, highlight color:{46516, 54741, 65535}, class:appearance preferences object, smooth scrolling:false, font smoothing style:automatic}

set properties to {scroll arrow placement:together at top and bottom, font smoothing limit:4, recent applications limit:10, scroll bar action:jump to here, double click minimizes:true, recent servers limit:20, appearance:blue, recent documents limit:20, highlight color:{0, 0, 32000}, smooth scrolling:true, font smoothing style:light}

end tell

end tell

It looks promising, but those properties are obviously for an older version of OSX. Since I'm so new to this, I don't know how to define a new property to modify. This is what I tried (which didn't work):

tell application "System Events"

tell appearance preferences

get properties

set properties to {Use dark menu bar and Dock:true}

end tell

end tell

This also didn't work (all I did was add quotation marks in line 4):

tell application "System Events"

tell appearance preferences

get properties

set properties to {"Use dark menu bar and Dock":true}

end tell

end tell

Any ideas as to how to do this? Once I have this AppleScript written, I can easily throw it into Automator to make it change with the time of day. I can't wait! Any help is greatly appreciated. Have a wonderful day!