Text color changes according to background color

[Salman0D4D]

When I add a rectangle behind the text, the text color being c=0, m=0, y=0, k=100, and rectangle color is c=10, m=10, y=0, k=0. When i export it, the text color becomes c=10, m=10, y=0, k=100. Why is this happening?
In the picture attached, u can see the text color difference on the colored rectangle and white rectangle.

[rob day · Accepted solution]

By default the [Black] swatch overprints. You can either make a new black only swatch—new colors knock out unless you change the overprint in the Attributes panel—of you can change the [Black] Overprint setting in Preferences>Appearance of Black. Normally you would want small text to overprint if the destination is an offset press.