いっそObjImageでオーナードロー気味に描画しちゃうのはどうでしょうか?
*Main
Font msGothic, 16, 16 :SysColor 15 :BoxF ;下準備
sBtn = "ちぇっくぼっくす?","☆","★" :iBtn = 0
SysColor 18 :Pos 22, 422 :Mes sBtn
SysColor 26 :Pos 22, 442 :Mes sBtn :Pos 22, 462 :Mes sBtn
GradF 220, 420, 20, 20, 1, $400000, $000000
GradF 220, 440, 20, 20, 1, $FF0000, $400000
Color :BoxF 240, 420, 259, 459
HsvColor ,,255 :Pos 242, 422 :Mes sBtn.1 :Pos 242, 442 :Mes sBtn.2
gMode 7, 20, 40 :Pos 200, 420 :gCopy 0, 220, 420 :gMode 0, 20, 20
Repeat 3 :Pos 0, cnt*20+420 :gCopy 0, 200, 420 :Loop
ObjSize 170, 20 :ObjImage 0, 0, 420, 0, 440, 0, 460
Pos 4, 4 :Button "", *chk_button :ObjImage -1
Stop
*chk_button
i = stat :iBtn ^= 1
Repeat 3 :Pos 0, cnt*20+420 :gCopy 0, 200, iBtn*20+420 :Loop
SendMsg hWnd, 6, 1 :ObjSel i ;フォーカス再設定で表示更新
Stop