Click on Resize and set to pixels and uncheck the "maintain aspect ratio" box. Then set the canvas size to 1000 x 800.
Zoom in to 500% using the slider at the bottom right of the window.
Choose the Right Triangle shape. Make the Size the thinnest one.
Keep the default colors. Make sure Outline is set to "Solid color", and Fill is set to "no fill".
CORRECT:Hold SHIFT and click & drag out a triangle.
INCORRECT: If you let go of SHIFT before you're done, you'll get a crooked triangle. Delete and try again!
Don't make it too big, you'll need to fit 3 more in that space at 500%.
Make sure the Select tool is set to "Transparent".
Click on the rectangle Select button and click and drag around the triangle to select it.
Make sure they meet with one-pixel space between!
Paste again, then Rotate>Flip Horizontal, and move into place with the bottom one.
Paste one last time, then Rotate>Rotate 180 degrees, and move into place.
Fill in the bottom-left and upper-right triangles with one color. Fill the other opposite triangles another color.
Do NOT fill any sides with black!
Zoom out to 400%. Select the top square, a little extra around it and move it up to the top left corner of the canvas, leaving a decent margin.
Make sure the black one-pixel border of the copy lines up and fits between the other triangles!
So it looks like this...
Now select all (CTRL+A) and copy (CTRL+C) and paste (CTRL+V). And move it down and into place so it fits.
Make sure they are lined up!
Continue the pattern of:
Continue until you complete 2 columns of squares from the top to the bottom.
Then scroll a bit to the right and up to the top.
Repeat the process, moving over to empty space before pasting until you've filled the entire canvas.
Then zoom out to 100%.