Very light grey, almost white, with a smidgen of pale yellow in it. Give a bit of adobe wall a light dry brushing and see what you think, you can always add more, till you're happy with the look.
Worse case scenario is they finish up looking like this!
(http://leadadventureforum.com/index.php?action=dlattach;topic=90474.0;attach=60642;image)
(http://leadadventureforum.com/index.php?action=dlattach;topic=100341.0;attach=60739;image)
(http://leadadventureforum.com/index.php?action=dlattach;topic=100341.0;attach=60746;image)
:)
Just like Rob says, it's dead easy... when you know how!
The OK sign was printed onto buff coloured paper, then cut in strips to look like planking, the strips are then glued onto a cardboard base. You give the sign a wash of really thinned down brown paint, and job's a good 'un...
(https://www.thewargameswebsite.com/wp-content/uploads/hm_bbpui/123429/3v1rqvk52pg805yivj31ur74rqgtr0q5.jpg)
;)