MacVim gets all settings from ~/.vimrc, but not the colors and I have to source it again

Question

I am using the following ~/.vimrc with MacVim 7.4 on MacOS X Mavericks:

set guifont=Menlo:h14
set encoding=utf8
set mouse=a
set expandtab
set ts=8
set showcmd
set nocompatible
set backspace=2
set viminfo='20,\"50
set history=50
set ruler
set si
set hlsearch
syntax on
set bg=light
hi Cursor     term=inverse   ctermfg=black                guifg=black  guibg=green
hi Visual     term=inverse   ctermfg=yellow ctermbg=black guifg=yellow guibg=black
hi Comment    term=inverse   ctermfg=grey   ctermbg=black guifg=white  guibg=black
hi Identifier term=NONE      ctermfg=black                guifg=black
hi Constant   term=underline ctermfg=darkred              guifg=red
hi Statement  term=bold      ctermfg=blue                 guifg=blue
hi PreProc    term=NONE      ctermfg=black                guifg=black  gui=underline
hi Special    term=NONE      ctermfg=black                guifg=black
hi Type       term=bold      ctermfg=blue                 guifg=blue

and can see that the editor takes all the settings from that file (the font family and its size, the show ruler and tab settings, ...), but not the colors:

Only after I issue the command :so ~/.vimrc does it take my color settings too (red and blue with inverted comments):

Does anybody please know, what is happening, why doesn't MacVim pick up the syntax colors too?

Below is the :version information:

VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Aug 10 2013 18:40:52)
MacOS X (unix) version
Compiled by Douglas Drumond <[email protected]>
Huge version with MacVim GUI.  Features included (+) or not (-):
+arabic          +emacs_tags      +localmap        +postscript      +textobjects
+autocmd         +eval            -lua             +printer         +title
+balloon_eval    +ex_extra        +menu            +profile         +toolbar
+browse          +extra_search    +mksession       +python          +transparency
++builtin_terms  +farsi           +modify_fname    -python3         +user_commands
+byte_offset     +file_in_path    +mouse           +quickfix        +vertsplit
+cindent         +find_in_path    +mouseshape      +reltime         +virtualedit
+clientserver    +float           +mouse_dec       +rightleft       +visual
+clipboard       +folding         -mouse_gpm       +ruby            +visualextra
+cmdline_compl   -footer          -mouse_jsbterm   +scrollbind      +viminfo
+cmdline_hist    +fork()          +mouse_netterm   +signs           +vreplace
+cmdline_info    +fullscreen      +mouse_sgr       +smartindent     +wildignore
+comments        -gettext         -mouse_sysmouse  -sniff           +wildmenu
+conceal         -hangul_input    +mouse_urxvt     +startuptime     +windows
+cryptv          +iconv           +mouse_xterm     +statusline      +writebackup
+cscope          +insert_expand   +multi_byte      -sun_workshop    -X11
+cursorbind      +jumplist        +multi_lang      +syntax          -xfontset
+cursorshape     +keymap          -mzscheme        +tag_binary      +xim
+dialog_con_gui  +langmap         +netbeans_intg   +tag_old_static  -xsmp
+diff            +libcall         +odbeditor       -tag_any_white   -xterm_clipboard
+digraphs        +linebreak       +path_extra      -tcl             -xterm_save
+dnd             +lispindent      +perl            +terminfo
-ebcdic          +listcmds        +persistent_undo +termresponse
   system vimrc file: "$VIM/vimrc"
     user vimrc file: "$HOME/.vimrc"
 2nd user vimrc file: "~/.vim/vimrc"
      user exrc file: "$HOME/.exrc"
  system gvimrc file: "$VIM/gvimrc"
    user gvimrc file: "$HOME/.gvimrc"
2nd user gvimrc file: "~/.vim/gvimrc"
    system menu file: "$VIMRUNTIME/menu.vim"
  fall-back for $VIM: "/Applications/MacVim.app/Contents/Resources/vim"
Compilation: clang -c -I. -Iproto -DHAVE_CONFIG_H -DFEAT_GUI_MACVIM -Wall -Wno-unknown-p
ragmas -pipe  -DMACOS_X_UNIX -no-cpp-precomp  -g -O2 -U_FORTIFY_SOURCE -D_FORTIFY_SOURCE
=1
Linking: clang   -L.    -L.     -L/usr/local/lib -o Vim -framework Cocoa -framework Carb
on       -lncurses  -liconv -framework Cocoa   -fstack-protector -L/usr/local/lib  -L/Sy
stem/Library/Perl/5.12/darwin-thread-multi-2level/CORE -lperl -lm -lutil -lc -framework
Python   -framework Ruby

Answer 1

MacVim is sourcing its default gvimrc after your ~/.vimrc. It contains this snippet:

" Load the MacVim color scheme.  This can be disabled by loading another color
" scheme with the :colorscheme command, or by adding the line
"   let macvim_skip_colorscheme=1
" to ~/.vimrc.
if !exists("macvim_skip_colorscheme") && !exists("colors_name")
    colorscheme macvim
endif

What happens is simple: MacVim's default colorscheme overrides your :hi commands when you launch Vim and your :hi commands override the default colorscheme when you source ~/.vimrc.

The fix is simple too: turn your :hi commands into a real colorscheme as per Ingo's answer.

Also, set background=light is only useful in a colorscheme so move that line as well.