the entire painting industry has started using shades of gray for sealer, we have white and black and mix it to the desired shade that will give the paint the best coverage. believe it or not, red paint doesn't cover red primer very well but it will cover the proper shade of gray with ease. for the IH red id recommend something around the charcoal or dark charcoal, if the primer is to light it will either take a lot of coats to cover or it will look good inside but pink outside in the sun.
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