We have two film adaptations of Gil-galad: Lord of the Rings (which was cut, but we know he exists) and Rings of Power. And neither of these film adaptations matches Gil-galad!!

I want to talk about his appearance now, specifically that in both film adaptations, Gil-galad has dark hair and a gold color in his design.

The book Gil-galad, despite being from the Golden House of Finarfin, has silver hair.

Also, Gil-galad's entire image is associated with silver. And that's why the gold color in both designs doesn't match Tolkien's vision of Gil-galad.

Let me explain about silver:

1. Silver hair

2. Silver armor and shield, thanks to which Ereinion was given the epessë Gil-galad, which means 'star of radiance.'

As in the name Gil-galad 'star of radiance' given to Finwain, last High-king of the Eldar, because of the radiance of his silver hair, armor, and shield that, it is said, could even in the moonlight be seen from many leagues afar.

-The Nature of Middle-earth, Part Two: IV Hair

Even the poem about the Fall of Gil-galad mentions this:

His sword was long, his lance was keen,

his shining helm was seen afar;

the countless stars of heaven's field

were mirrored in his silver shield.

- LotR: The Fellowship of the Ring, A Knife in the Dark

3. Gil-galad's heraldry features silver stars (he himself is like a silver star)

4. Aeglos (Gil-galad spear) means 'snow-point' or 'icicle.' The element aeg means 'point,' from the root AYAK ('sharp, pointed'); and the element los means 'snow.'

This is referring to a winter theme, and winter is associated with white/silver and blue (colour of Gil-galad's heraldry).

The book Gil-galad is a solitary silver star ('solitairy' because he never married) who led his people and fell in Mordor.

But long ago he rode away,

and where he dwells, none can say;

for into darkness he fell his star

in Mordor where the shadows are.

- LotR: The Fellowship of the Ring, A Knife in the Dark