That tutorial is wrong. Using Envelope Distort > Make with Mesh does not allow you to select mesh points and color them.
You are not doing anything wrong, the tutorial is inaccurate.
After drawing the box... choose Object > Create Gradient Mesh That will convert the box to a Mesh object which has anchors you can then assign colors to.
I'm using CS5 on Windows 10 and am having an issue with the gradient mesh colors.
Here's a sample of a gradient mesh I'm working with and the problem I'm experiencing. http://imgur.com/ImY4gWU
I'm trying to figure out why this is blending from the red (or blue) to gray and then to black. I'm wanting this to blend directly from the color at the anchor to black without that odd gray in the transition. I haven't done anything more complicated than create the mesh, select an anchor and change the color of that anchor. I'm trying to create a smooth glowing effect, which I've been able to do previously, but can't figure out what's going wrong this time and why it's not blending how I want it to.
Tutorial for how to make this gradient mesh? but instead of black i want it to go to transparent. Is that possible? I am trying to make a golden glow for an egg...
How do I modify this colored Mesh in Illustrator? - Graphic Design Stack Exchange
Gradient Mesh Color Blending With Unwanted Gray?
does anyone know how to recolor this mesh? i tried the recolor option but it doesn't work :/
Videos
One way of doing it would be by inverting colors. First expand artwork.
select the artwork >Edit >Edit Colors>Invert colors
This way your black areas become white. But you will have to recolor artwork after, since colors other than black and white turn into other colors on inverting .
Its hard to tell exactly but I'm almost 100% sure that you should look into Appearance panel (Shift+6) or (Window>Appearance), and check blending modes.
Without examining file it will be hard to tell :)