Yeah I know this book is basically dead but anyways...
Spirit and Askar were meant to be opposites in the story. If you don't get what I'm saying, they're meant to be very different to each other (kinda like poppy and branch's relationship if you think about it).

Spirit is determined, curious and outgoing while Askar is shy, nervous and actually looks before he leaps!
Even their color schemes and designs are supposed to be different:

Askar has a neutral gray tone in his fur and bright orange/golden eyes

While Spirit has a more cool-gray tone to her fur with blue eyes (complete opposite to Askar's)

But I didn't just make these differences just cuz I have no color sense - I did it because it really shows that these 2 characters are almost completely different and yet they have one of the strongest relationships in the story, which I guess you can say really builds up their friendship and shows that differences don't really matter :)