Eaves soffits discoloring, investigating causes

hello everyone,

this is my first post here and I would be glad if you could help me. if information is missing, please let me know.

briefly about my issue:

we started building the house at the end of 2017. the roof including the soffits made of three-layer wood panels was completed in mid-December 2017. since last autumn, I have noticed discolorations on the soffits. these can be seen all around the house. sometimes more, sometimes less. so far, I can’t make a 100% conclusive sense of it. the shell builder, who installed the soffits and the roof, just said "it’s wood after all." our architect mentioned the issue of moisture. the question is where it comes from.

the structure of the entire roof, from inside to outside, is as follows:

drywall ceilings

vapor barrier foil

24 cm rafters with insulation between rafters

6 cm soft fiberboard

dörken delta foxx underlay membrane

counter battens / lathing

nelskamp f 8 1/2 tiles

the soffits are screwed truss-side to the counter battens of the lathing, gable-side the lathing was used for fastening. the underlay membrane also lies on the soffits.

the soffits were primed by the shell builder. however, as it seems to me, only on the visible side. not on the end sides or top. the plasterer then painted twice with acrylic paint. that’s what he says. I was not present. at the moment, I cannot prove otherwise.

I took some pictures and hope they show something. on the one hand, you can see the yellowish / brownish discolorations. on the other hand, hopefully, you can see that the individual strips of the 3S panels are partly very clearly visible.

did "only the wood absorb the color" or is there possibly something bigger behind this?

I look forward to your replies and thank you in advance

I don't believe the color has disappeared into the wood, but rather the opposite. Namely, that what is visible comes from the wood: residual moisture and resin, which have worked through after 3 years. It shouldn't be a drama - but also not a case for a complaint. Nevertheless, it doesn't look like three coats.