Pigment production is usually more sparse in kittens than in adults, and most often any change of colour will be to darken rather than lighten. There's quite a difference between my Sonic at 3 months and Sonic now at over a year old - he's blue (the changes can be most noticeable in dilutes, if you exclude colourpoints) and has gone from a mid-grey to a dark steel blue as he's got his beautiful adult coat through.
Also the rufous colour in tabby (all patterns) cats can take a while to come in. I don't know how much rufous is usually in Norwegian Forest cat tabbies. It's the red or rust red undertone in the coat.
My bengal has changed from having an almost yellow coat with her tabby markings to now at 2 years old having a rich auburn base coat.
Her face as a kitten and then now. You can see a big colour difference.