How to change the color of the scroll bar?

A bit late, but perhaps I've found a quite nice, easy GUI solution:

gnome-color-chooser

Highlights:

• Completely GUI solution, no need to manually fiddle with ~/.gtkrc
• Only changes the settings you check. Uncheck them revert to default.
• Changes are applied as soon as you click Apply. No need to switch themes back and forth
• No need of sudo (but changes are to your user only)
• Applies to "legacy" scrollbars only (the ones that need to be fixed). The "overlay" scrollbar is not modified.

The changes are quite unobtrusive: it edits (or creates) ~/.gtkrc to include its own config file:

include ".gtkrc-2.0-gnome-color-chooser"

And that file is pretty slim too:

style "gnome-color-chooser-scrollbar"
{
  bg[NORMAL] = "#ACACAC"
  bg[PRELIGHT] = "#808080"
  bg[ACTIVE] = "#ACACAC"
}
widget_class "*Scrollbar" style "gnome-color-chooser-scrollbar"

Btw, I've picked the above colors out of experiments. They blend in nicely with Ambiance's "monochrome-ish" style, being just a bit darker (and thus more visible) than default.

Until Firefox gets overlay scrollbars, I'm quite happy with my custom colors :)

I built upon what culebrón described and accidentally created something I think is pretty awesome...

Open /usr/share/themes/Ambiance/gtk-2.0/gtkrc as root for modification:

gksu gedit /usr/share/themes/Ambiance/gtk-2.0/gtkrc

Then modify the matching section in that file to the following (remember to back up the defaults in case you don't like the changes):

style "scrollbar" = "button" {
    xthickness = 2
    ythickness = 2

    bg[NORMAL] = shade (0.62, @bg_color)
    bg[PRELIGHT] = shade (0.66, @bg_color)

    bg[ACTIVE] = shade (0.64, @bg_color)

    engine "murrine"
    {
        border_shades = {0.95, 0.90}
        roundness = 3
        contrast = 1.0
        trough_shades = {0.92, 0.98}
        lightborder_shade = 1.3
        glowstyle = 5
        glow_shade = 1.02
        gradient_shades = {1.2, 1.0, 1.0, 0.86}
        trough_border_shades = {0.9, 0.98}
    }
}

Save, then apply the changes by toggling themes or logging out.

The new, awesome, and usable scrollbars might look like:

The above changes the scroll bar for applications that use the gtk2 theme files. So does the gnome-color-chooser, (atleast the one in the current repository). For gtk3 applications, like gnome-terminal and gedit in 13.04 using gnome-fallback, one needs to change /usr/share/themes/Ambiance/gtk-3.0/gtk-widgets.css.

To do this

sudo gedit /usr/share/themes/Ambiance/gtk-3.0/gtk-widgets.css

and replace the * scrollbar * section with this:

/*************
 * scrollbar *
 *************/
.scrollbar,
.scrollbar.vertical {
    -GtkScrollbar-has-backward-stepper: 0;
    -GtkScrollbar-has-forward-stepper: 0;
    -GtkRange-slider-width: 14;

    border-radius: 3px;

    border-image: none;
}

.scrollbar.trough,
.scrollbar.trough.vertical {
    border-color: shade (@bg_color, 0.64);
}

.scrollbar.trough.horizontal {
}

.scrollbar.slider,
.scrollbar.slider:hover,
.scrollbar.button,
.scrollbar.slider.vertical,
.scrollbar.slider.vertical:hover,
.scrollbar.button.vertical {
    border-width: 1px;
    border-style: solid;
    border-color: shade (@bg_color, 0.4);
    background-image: -gtk-gradient (linear, left top, right top,
                                     from (shade (@button_bg_color, 0.76)),
                                     to (shade (@button_bg_color, 0.62)));
    box-shadow: inset 1px 0 shade (@button_bg_color, 0.85),
                inset -1px 0 shade (@button_bg_color, 0.62),
                inset 0 1px shade (@button_bg_color, 0.9),
                inset 0 -1px shade (@button_bg_color, 0.62);
}

.scrollbar.slider.horizontal,
.scrollbar.slider.horizontal:hover,
.scrollbar.button.horizontal {
    background-image: -gtk-gradient (linear, left top, left bottom,
                                     from (shade (@button_bg_color, 0.76)),
                                     to (shade (@button_bg_color, 0.62)));
    box-shadow: inset 1px 0 shade (@button_bg_color, 0.85),
                inset -1px 0 shade (@button_bg_color, 0.62),
                inset 0 1px shade (@button_bg_color, 0.9),
                inset 0 -1px shade (@button_bg_color, 0.62);

}

.scrollbar.button,
.scrollbar.button:insensitive {
}

This gives a scrollbar in gtk3 that looks like this:

Which is kinda similiar to the one for gtk2 above. The small ticks and proper steppers is not included here though.