Yes, if you are mailing in your tax return to the IRS, it must be printed in black ink on white paper, or the same color that the offical IRS form is printed on.
Here's an excerpt from IRS Puplication 1167:
"It's preferred that the color and opacity of paper substantially duplicate that of the original form. This means that your substitute must be printed in black ink and may be on white paper or on the colored paper the IRS form is printed on."
The official IRS Form 1040 is printed in black ink on white paper with some blue shading, so tan wouldn't be an acceptable paper color.
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