Canon EOS 750D Instruction Manual page 195

You can display the histogram by pressing the <B> button. However,
the histogram is not displayed while pressing the shutter button
completely.
When <g> is displayed in white, it indicates that the Live View image
brightness is close to what the captured image will look like.
If <g> is blinking, it indicates that the Live View image is displayed at
a brightness that differs from the actual shooting result because of low-
or bright-light conditions. However, the actual image recorded will reflect
the exposure setting. Note that noise may be more noticeable than the
actual image recorded.
If the <F> or <G> shooting mode, Multi Shot Noise Reduction, flash, or
bulb exposure is used, the <g> icon and histogram will be grayed out
(for your reference). The histogram may not be properly displayed in low-
or bright-light conditions.
Do not hold the camera in the same position for long periods of time.
Even if the camera does not feel too hot, prolonged contact with the same
body part may cause skin redness, blistering or low-temperature contact
burns. Using a tripod is recommended for people with circulation problems
or very sensitive skin, or when using the camera in very hot places.
A Shooting with the LCD Monitor
195