DEVICES, METHODS AND GRAPHICAL USER INTERFACES FOR DISPLAYING AN AFFORDANCE ON A BACKGROUND

An electronic device with a display and a touch-sensitive surface displays, on the display, content and an affordance, wherein: the affordance is displayed over a portion of the content; a value of a display property of the affordance is determined based a value of the same display property of the portion of the content over which the affordance is displayed; and the value of the display property of the content is permitted to vary within a first range of values, and the value of the display property of the affordance is constrained to vary within a second range of values that is smaller than the first range of values; while displaying the content and the affordance, the device detects a change in appearance of the content over which the affordance is displayed; and in response to detecting the change in appearance of the content over which the affordance is displayed, the device changes the appearance of the affordance, including: in accordance with a determination that the value of the display property of the content has decreased, increasing the value of the display property of the affordance in accordance with a magnitude of a change in the value of the display property of the content and the second range of values; and in accordance with a determination that the value of the display property of the content has increased, decreasing the value of the display property of the affordance in accordance with a magnitude of the change in the value of the display property of the content and the second range of values.