[ltk-user] Scale command option help

Hello, I was wondering if someone could tell me where I'm going wrong in my code:

(defun nomogui () (with-ltk () (let* ((s0 (make-instance 'scale :label "X-ri" :digits 6 :orientation 'horizontal :troughcolor "#000099" :resolution .001 :from 1.4 :to 1.6)))

(configure s0 :command (lambda (val) (print 'hello) (if (< 1.5 val) (configure s0 :troughcolor "#990000") (configure s0 :troughcolor "#009900")))) (pack s0))))

Basically I just want to be able to change the troughcolor of the scale based on its value. Any help?