provide the color structs using (provide (struct-out ...))

closes PR 9867

collects/htdp/color-structs.rkt

@@ -0,0 +1,5 @@
+#lang racket/base
+(provide (struct-out color)
+         (struct-out alpha-color))
+(define-struct color (red green blue) #:transparent)
+(define-struct alpha-color (alpha red green blue) #:transparent)

collects/htdp/htdp.scrbl

@@ -2,6 +2,7 @@
 
 @(require scribble/manual 
           (for-label [except-in racket require]
+                     htdp/color-structs
                      [only-in lang/htdp-beginner require]))
 
 @title[#:style 'toc #:tag "htdp"]{Implementing HtDP Teachpacks, Libraries, and Customized Teaching Languages}
@@ -58,3 +59,16 @@ of DrRacket's teaching languages.
 @include-section["error-reporting.scrbl"]
 @include-section["testing.scrbl"]
 @include-section["htdp-lib.scrbl"]
+
+@section{Color and Alpha Color Structs}
+
+@defmodule[htdp/color-structs]
+
+@defstruct[color ([red any/c] [green any/c] [blue any/c])]{
+  This is the color sturct that is also exported by @racketmodname[htdp/image],
+  but here it is exported via @racket[(provide (struct-out color))].
+}
+@defstruct[alpha-color ([alpha any/c] [red any/c] [green any/c] [blue any/c])]{
+  This is the color sturct that is also exported by @racketmodname[htdp/image],
+  but here it is exported via @racket[(provide (struct-out alpha-color))].
+}

collects/htdp/image.rkt

@@ -16,6 +16,7 @@ plt/collects/tests/mzscheme/htdp-image.rkt
          lang/prim
          lang/posn
          lang/private/imageeq
+         "color-structs.rkt"
          "error.rkt")
 
 (provide-primitives
@@ -77,9 +78,6 @@ plt/collects/tests/mzscheme/htdp-image.rkt
 (define (alpha-color-list? l)
   (and (list? l) (andmap alpha-color? l)))
 
-(define-struct color (red green blue) #:inspector (make-inspector))
-(define-struct alpha-color (alpha red green blue) #:inspector (make-inspector))
-
 ;; ----------------------------------------
 
 (define (to-exact-int x) (floor0 (if (exact? x) x (inexact->exact x))))