Found text does not show at all highlighted on some text colors (like green and orange) when using the find button in the replace dialog box when box is open/visible.

Then when dialog box is closed it will highlight the found text in black on gray like 'selected' and not in white on black 'found' highlighting color scheme.

Using F3, to find text, highlights in black on gray like 'selected' and not in white on black 'found' highlighting color scheme

Also using CTRL+f to find text seems to follow the same improper behavior, just less noticeable since as soon as find button is pressed, the dialog box is closed and the found text is shown, but if the dialog box would not close the text would not be shown with any highlighting at all ('found' nor 'selected' highlighting).

To test the last behavior I used the find_keep_open.patch to prevent CTRL+f Find Dialog box to close after pressing find button.(issue13586)

Note: 
Color scheme highlighting setting can be seen in IDLE Preferences pane under the Highlighting tab by going to Options/Configure IDLE...