How do you make a white background for YouTube videos?

You are right "afterwards, it's almost like a weird color of beige". It happens because of light. As you did not mention what kind of light are you using therefore, have to use wild guess to answer you. Yobuscus might be using professional lights during video recording. But no need to buy costly light you could try using LED lights or tube lights. The secret of lighting is balance. If you are in the middle use two lights in front 45 degrees. The front two lights should not be straight rather both should be 45 degrees angle each. Diffuse light will not create shadow. To avoid shadow cover the light with some kind of diffusing stuff but be careful if the lights are hot. I know what I am saying must be difficult to understand but you got to try and see. This is how we all learn. You may use url link to read some details and better search that website. You will learn something. IF you need any further help send message or mail. Additional: Hope if you follow above guidance your white background a white paper or bed sheet will appear as white.