WC_SPLITPANE colors

The splitpane colors are customizable via the presentation parameters.
The colors used by a splitpane are:
Background color (default pale grey - 0xcccccc)
used to paint the splitter background, is modifiable via the PP_BACKGROUNDCOLOR and PP_BACKGROUNDCOLORINDEX presentation parameters.
Foreground color (default black - 0x000000)
used to paint the hide-pane arrows, is modifiable via the PP_FOREGROUNDCOLOR and PP_FOREGROUNDCOLORINDEX presentation parameters.
Hilite color (default white - 0xffffff)
used both to for the light color of the pattern which overlays the splitter and the hide-pane arrows when activated by the mouse, is modifiable via the PP_BORDERLIGHTCOLOR presentation parameter.
Shadow color (default dark grey - 0x808080)
used both for the dark part of the pattern overlaying the splitter and for the disabled hide-pane arrows, is modifiable via the PP_BORDERDARKCOLOR presentation parameter.