i don't understand why Sometimes the menu loaded as chdk default color orange and Sometimes grey as i changd it
The colors in the CHDK menu change depending on what the Canon firmware has displayed on the LCD. They will change depening on whether you are in playback or shooting mode and if you have the Canon menu active. This is because the camera's firmware changes the color pallette entries when it changes mode and CHDK is unable to detect / correct for that.
Note that CHDK for a few recent cameras have code to create custom colors just for CHDK's use.
and how do i load chdk default menu
Normally, you just press the Menu button while in <ALT> mode to load the CHDK default menu. If you are asking how you reset CHDK, go to the Miscellaneous menu and use the reset option there. Or delete any file with a .CFG extension in the CHDK directory on your SD card.