Overprint simulation failing on export

If this is going to print with PMS and you need tiff export only for preview:
- use CMYK preview for PMS 295 which not includes K in it

- use multiply for top object

- if still lacks of contrast use double multiply (in appearance panel set once fill to multiply and object to multiply).

All 4 setups (including only K set on overprint ) will lead to same printing resutl and pretty defferent previews on screen.

You can use whatever suits best but don't judge printing results on screen.

If PMS is not supposed to print and you are using color books just as palette for easy picking shades of colors then the easiest way in your case is just to measure with eyedropper the screenshot of you illustrator preview and use RGB/CMYK values

Luke is correct, your spot color, when converted to process contains black and the top 25% black will not overprint.

PNG and JPEG do not support spot colors or overprint.

Overprint  is used with printing inks (as the name overPrint) suggests.

Overprinting a spot ink is a special case because it is not a standard process CMYK ink.

When spot colors have to be converted to CMYK, to display them in an RGB or CMYK image file format, the rules for overprinting CMYK inks will be applied.

It quickly becomes complicated to understand the behaviour of overprint when the top color contains a percentage of an ink that is also part of the underlying color, it will not overprint that shared ink.

Multiply instead of Overprint is the best solution and modern rips will separate spot colors set to Multiply as good as spot colors set to Overprint. They behave actually better when spots are converted to process inks, as your example shows.

Have a look at this document that shows the interaction of colors set to Overprint with the underlying colors.

https://adobe.ly/39Y98hD

I also tried Pantone 286 and it works just fine. Is Illustrator somehow looking at a minimum density variation between an overprint and Pantone color? If I bump the black to 50%, then it will overprint Pantone 295 just fine. But anything below 50% appears lighter.

This is super crazy. I run into the same issue testing with Pantone 295, but if I use a different Pantone color, say PMS 2130 or PMS 130, then it shows the overprint properly on the jpeg or tiff that is exported out.

You should convert the PMS 295 to 4C before exporting to an image.

You will notice the PMS 295 converts to a black that is greater than 25%, so overprinting won't work.

Set the 25% black to multiply.