/etc/X11/app-defaults/XCal is in xcal 4.1-19.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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!
!	Help filename if not using internal text
!XCal.helpFile: /usr/X11/lib/X11/app-defaults/XCal.help
!
!	Data format strings
!	I use these on my Sun - uncomment if your system supports
!	%e in strftime formats
!XCal.format: %A %e %B %Y
!XCal.editFmt: %A %e %B %Y
!XCal.already: Already editing %e %B %Y
!
!	Geometry
XCal.edit.geometry: 325x150
XCal.memo.geometry: 325x300
XCal.alarm.geometry: 325x100+0+150
XCal*help.geometry: 600x300
!
!	Fonts
XCal.fontToday: lucidasanstypewriter-12
XCal*Font: lucidasanstypewriter-12
XCal*info.Font: lucidasans-10
XCal*alarmText*Font: 12x24
!
! Top level dialogs
XCal*newdate.Label: Enter mmm yyyy?
XCal*newdate.ok.Label: OK
XCal*newdate.cancel.Label: Cancel
XCal*exit.Label: Really exit?
XCal*exit.yes.Label: Yes
XCal*exit.no.Label: No
XCal*noedit.ok.Label: OK
!
! Strips & edit windows
XCal*back.Label: <
XCal*quit.Label: Quit
XCal*next.Label: >
XCal*help.Label: Help
XCal*save.Label: Save
XCal*edit.quit.Label: Quit
XCal*edit.help.Label: Help
XCal*text.scrollVertical: WhenNeeded
XCal*text.scrollHorizontal: WhenNeeded
XCal*text.autoFill: True
! Popups from the edit windows
XCal*check.Label: Save file?
XCal*check.yes.Label: Yes
XCal*check.no.Label: No
! Alarms
XCal*alarmText*scrollVertical: WhenNeeded
XCal*alarmText*wrap: word
XCal*alarmQuit.Label: Unpin
XCal*alarmHold.Label: Stick
! Memo box
XCal*display.scrollVertical: WhenNeeded
XCal*display.scrollHorizontal: WhenNeeded
XCal*display.cursor: dot
XCal*memoTitle.Label: Edit the memo file
XCal*weeklyEdit.Label: Edit
XCal*weeklyTitle.Label: Today's regular events
XCal*edit.Label: Edit
XCal*memocheck.Label: Save memo file?
XCal*memocheck.yes.Label: Yes
XCal*memocheck.no.Label: No
XCal*memoText.scrollVertical: WhenNeeded
XCal*memoText.scrollHorizontal: WhenNeeded
! Help
XCal*helpText.scrollVertical: Always
XCal*helpText.scrollHorizontal: WhenNeeded
XCal*helpText.autoFill: True
XCal*help*helpQuit.Label: Quit
!
! Colours from pc - not convinced about this, I need to live with a 
! colour screen for a bit to see what should be done
!
!XCal.MarkBackground:		wheat1
!XCal*background:		wheat1
!XCal*foreground:		black
!XCal*quit.foreground:		black
!XCal*quit.background:		wheat2
!XCal*edit.foreground:		black
!XCal*edit.background:		wheat2
!XCal*weeklyEdit.foreground:	black
!XCal*weeklyEdit.background:	wheat2
!XCal*next.foreground:		black
!XCal*next.background:		wheat2
!XCal*back.foreground:		black
!XCal*back.background:		wheat2
!XCal*help.foreground:		black
!XCal*help.background:		wheat2
!XCal*save.foreground:		black
!XCal*save.background:		wheat2
!XCal*yes.foreground:		black
!XCal*yes.background:		wheat2
!XCal*no.foreground:		black
!XCal*no.background:		wheat2
!XCal*helpQuit.foreground:	black
!XCal*helpQuit.background:	wheat2
!XCal*header.foreground:		black
!XCal*header.background:		wheat2
!XCal*Sun*Label*background:	wheat2
!XCal*Sat*Label*background:	wheat2
!
! Colours from reed wade@cs.utk.edu
!
!XCal*background:        LightSteelBlue
!XCal*foreground:        SaddleBrown
!XCal.MarkForeground: Black
!XCal.MarkBackground: CornflowerBlue
!XCal.edit.background: CornflowerBlue
!XCal.edit.foreground: OliveGreen
!XCal*exit.background: MediumTurquoise
!XCal*exit.foreground: SlateGrey
!XCal*check.background:  lavender
!XCal*help*background: wheat
!XCal*help*foreground: blue
!XCal*newdate*background: plum
!XCal*newdate*foreground: red
!XCal*quit.background:   SteelBlue
!XCal*quit.background:   green
!XCal*back.background: yellow
!XCal*next.background: yellow
!XCal*no.background: DarkKhaki
!XCal*yes.background: PapayaWhip
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