I know that crosses are a Northern European thing, Nordic crosses are a Nordic thing and that the Union Jack is made from England and Scotland's flags combined but wondered whether the colour scheme from Iceland's was chosen because of the Union Jack?
Never considered it before but I remembered that Iceland's original colonisers were supposedly Viking Men and Irish Women, and that Ireland was obviously represented under the Union Jack for a long time. So maybe a Nordic flag with "Irish" colours would be fitting and perhaps that would be why?
Sorry for asking if the answer is no.
The Union Flag/Jack was adopted by the Act of Union in 1801 and, according to the Flag Institute, uses the Pantone colours Blue 280, White and Red 186.
The Iceland flag was adopted by Article 1 of the Flag Act No. 34/1944 and the colours are described under the SCOTDIC system as Sky blue (nr. 693009), Snow white (nr. 95.) and Fire red (ICELAND FLAG RED). The Prime Minister's Office of Iceland states that the flag was first designed in 1906.
So it looks like the similarity in the colours is unintentional, as is the similarity in how the colours are laid out.