On the "Colour" page, when white colour is selected, its value written to ~/.claws-mail/clawsrc as #100100100. And everything goes wrong when parsing ... I can reproduce this with "quick search" background/text colour at least.
Thanks for reporting! Fixed in commit: https://git.claws-mail.org/?p=clawsker.git;a=commit;h=d9bbeeeae01ce28cf9cc91636f9630c1486532e7