How to plot color in 3D RGB color space?

Problem: Randomly select some colors from an sRGB image and plot them in 3D RGB color space having true RGB values as present in the image
***************************************************************************
The following code will pick some random 5% color from Fig1. Then it plots those colors in 3D RGB color space which is shown in Fig2. Enjoy!

Fig1: A test image named 'pepper.png' and we would like to plot some colors of this image into RGB color space

True RGB values in RGB color space coming from image (pepper.png)

Today's homework: Please convert this RGB colors into LAB color and plot in 3D Lab color space. 
Hint: Use makecform and applycform of MATLAB for color space conversion