Send a multipart email. Include the spam keywords in the text/plain part, and your ordinary message in the text/html part. Almost all email clients these days will ignore the text/plain part, so they'll only see the text/html and there won't be any suspicious 1pt white text. As long as they don't view the raw message, you should be in the clear.
Or even better, use base64 transfer encoding for the spam keywords. Spam filters HATE base64.
Send a multipart email. Include the spam keywords in the text/plain part, and your ordinary message in the text/html part. Almost all email clients these days will ignore the text/plain part, so they'll only see the text/html and there won't be any suspicious 1pt white text. As long as they don't view the raw message, you should be in the clear.
Or even better, use base64 transfer encoding for the spam keywords. Spam filters HATE base64.