Finding Specific Color range within area of an image

[SamRe]

Hello I am new to the ImageJ program and I am part of Science Research at my local High School. As part of my experimentation, I have a picture of an apple and need to be able to select an area and create a color range to find the area of pixels within a color range. First off, would it be possible to enter my own color range to measure and as well, would I be able to measure the pixels within a selected area of the color range I would like to use.