Internal error when getting pen% and brush% color

I happened to try this while looking into https://github.com/racket/gui/issues/307:

#lang racket/base

(require racket/class
         racket/draw)
(define p (new pen%))
(send p get-color)
(send p set-color "notacolor")
(send p get-color)

=>

(object:color% ...)
get-color: broke its own contract
  promised: (is-a?/c color%)
  produced: #f
  in: the range of
      the get-color method in
      brush%/c
  contract from:
      <pkgs>/draw-lib/racket/draw.rkt
  contract on: brush%
  blaming: <pkgs>/draw-lib/racket/draw.rkt
   (assuming the contract is correct)
  at: <pkgs>/draw-lib/racket/draw.rkt:85:19
  context...:
   /Users/bogdan/sandbox/racket/racket/collects/racket/contract/private/blame.rkt:346:0: raise-blame-error
   .../private/arrow-higher-order.rkt:375:33
   body of "/var/folders/11/9c7x7y096r9g35f9th6b93qc0000gn/T/tmp.ArY5q8ZT/draw.rkt"

The brush% class has the same issue.

Start with the contract at pkgs/draw-lib/racket/draw.rkt:85 and inspect the pen% and brush% get-color/set-color behavior. Run the Racket reproducer from the issue, including the invalid color, and compare both classes. Done means the reported operation no longer produces an internal contract error and its behavior is covered consistently for pen% and brush%.