Here is the final solution that I was able to use. I decided to layer a piece of mulberry paper on top of the postcard. The paper was a light peach color which I thought would give the card some nice color and contrast to the iridescent purple ink. I applied a thin coat of ModPodge to the postcard and placed the paper over it. After the paper dried, I Gocco printed the text is basic white. The interesting aspect of the final result is that the text is so faint that it is almost holographic in nature. You don't notice the text until the light hits the card at an angle. The glossy finish of the paint against the matte finish of the paper and card make this effect happen.
I then decided to see what would happen if I put ModPodge over the inked card. What happened was that the holographic nature of the text disappeared because there was no surface differential between the text and paper. In essence, the text gets lost in the glossy coating.
Finally, I decided to see what would happened if there was a colored variation/differential. In other words, would the text show up stronger if the top coating of ModPodge was tinted? So I poured out a small amount of ModPodge and tinted it with orange Dr. Ph. Martin watercolor concentrate. I had never thought about tinting ModPodge before but I figured two water based products should blend.
The tinting changed the overall color of the card which was fine. The holographic aspect of the text still disappeared but the text shows up better in the tinted card. I also had to tint the back of the card with ModPodge because some of the product edged under the card. I am not totally displeased with the results but I still like the holographic effect of the matte card. I will definitely use tinted ModPodge in the future.
The finished card with holographic effect.
The ModPodge layered card (without tinting).
The tinted ModPodge front.
The tinted back of the card.
P.S. the scan is much more yellow than it really appears. The card is really more of an apricot color.