I like the design.
I think it asks for a heavy saturation.
This card should look better with stronger colours as it represents something, a power. It needs to stand out from your regular game UI.
By keeping the frame of each card (the edge ornaments) the same, you can afford the variation brought by the strong colours because you remain consistent with the style of the game. Additionally, the players will most likely appreciate seeing their favourite cards or heroes with strong colours.
For illustrating my point, here's a comparison. If you increase the saturation by 90% and add some slight red colour to the middle tones:
As quick reference for theory and inspiration, I like to keep at hand this article from Valve on character art: http://media.steampowered.com/apps/dota2/workshop/Dota2CharacterArtGuide.pdf
Thank you for your kind comments, suggestions and your illustration! We really appreciate that you have taken the time to help us improve our game as the style and design is a big part of Eminence: Xander's Tales.
Funny you should mention Dota2 as we are massive fans of the game ourselves. The art guide was very educational and a pleasure to read through.
I agree that a stronger colours and saturation makes the image stand out and helps to represent a feeling of power. In fact, we have used this approach in the earlier stages of our development (keep your eyes pealed for concept art designs coming to our blog soon!)
However, after much consideration and feedback we have decided to go with a more subtle approach. The colour pallet, art direction and style that we are going for is very specific and will become a lot clearer as more cards (and more divisions!) and other elements of the game are revealed. Please keep an eye out at www.playeminence.com. We plan to release a new card design every Thursday.
Thanks again for your interest and support!