Change the selection color of Windows 7 32 bit without using any extra software. Here is how to do it.
Step 1
Open the partition where your Microsoft Windows 7 is installed. By default it is C drive. Now go to Windows > Resources > Themes. Like this:
---
You will see some files and folders there; right click over your current theme’s .theme file and open it with notepad:
You can click “Open it” and browse/select the Notepad executable
OR
If you find it difficult; just open the Notepad; click File > Select Open and change the file type to “all files” from”text files”:

Browse to Windows > Resources > Themes and select the .theme file you are using now; it will open with Notepad like this:

Step 2
Just scroll down a bit, you will find the string :
[Control Panel / Colors]
See this:

Why I am showing you a wrong screenshot? Because; I discovered not all theme files have this string! Infact, in 64 bit the string is absent in most of the theme files!
In 32 bit you will get this:
[ControlPanel/Colors]
HotTrackingColor=xyz abc pqr

Step 3
Now, you need a software to get the values for the colors.
Note that, a color may have double digit value not triple ; i.e., abc=52 xyz=34 pqr=78 ; the values represent RGB value.
You need a software to pick colors; I use ColorPic free software for this website and other graphical works. You can download it from here.

Step 4
Save the edited file in desktop or some convenient place. Just replace the original one with this one. Remember to save the file as “all files”.
Done. As you can see all the default blue color in the notepad screenshot has been changed to green.
Note: If you add the string in 64 bit; the colors of hyperlinks will be changed; not the selection colors.
Thanks to flexdaw for sharing this idea and the 32 bit screenshot has been used belongs to him.

This is great but still does not address the selection color inside windows explorer and similar places. They remain blue.
You have to Windows 7 Style Builder (WSB) for changing all without having any glitch. If we try to change without WSB, it becomes transparent :( in some areas. Anyway, the list:
In Windows 7 Style Builder > EExplorer & Shell > Explorer > ListView > ListItem > Selected,
that branch belongs to Windows Explorer.
And few more locations:
Lists, menus & tabs > menu > popupbackground
Lists, menus & tabs > menu > popupborders
Lists, menus & tabs > menu > popupcheck
Lists, menus & tabs > menu > popupcheckbackground
Lists, menus & tabs > menu > popupgutter
Lists, menus & tabs > menu > popupitem
Lists, menus & tabs > menu > popupseparator
Lists, menus & tabs > menu > popupsubmenu
By the way, WSB is paid software (but has a trial period too). Here is the official page:
http://vistastylebuilder.com/download.html#download
Hope it helps and thank you for the feedback and appreciation :)
In Control PanelColors:
Hilight changes the selection color.
ButtonFace changes the unfocussed selection color(and other things).