I did some trials of the kit spring against other losi springs by putting a kit spring on one shock and a Losi spring on the other with the same preload setting. Then with out oil I joined the ball ends together with a screw and pushing them together to see which bottomed out first. Repeated a few times and swapped hand to make it fair but i'm pretty confident this way works for me
I found that the front kit blue is almost the same as a Losi Red (within 1mm of each other). Losi Blue is significantly harder than the kit blue. The yokomo red is the same as a Losi Orange
For the rear the kit blue is the same as the Losi yellow and the kit yellow is only slightly softer than the kit blue (about 3mm difference) so probably the same as a Losi white (which i don't have to test against)
Try it if you have the springs and see what you think ( i use this method to check pairs of springs in case one has gone soft - when new they always meet at the same time so i'm happy this method is repeatable)