White gold is real gold alloyed with paler metals, then plated with rhodium for a bright white surface. The plating is what you see on a new ring: a clean, almost mirror white that makes diamonds look sharp and modern.
Underneath, the gold alloy is pale but a shade warmer than the rhodium. That is not a flaw, just how the metal is made, and it is the main reason to compare platinum before you buy.
Choose the width by looking at your engagement ring's band. Most women's bands fall around 2 to 3 mm, and a band close to the engagement ring's own width makes the pair look planned. A slimmer band lets an ornate engagement ring lead; a broader one makes the wedding band the statement, which suits wearing it alone.
Then check how the two sit together. Look at the pair from the side: under a raised head, a straight band can leave a gap, while a curved or notched shape tucks in close. Wider bands can feel tighter, so size for the width you plan to wear when you measure with the complimentary ring sizer Rare Carat mails out.
The two look almost identical when new, so a white gold band beside a platinum engagement ring works well. The difference appears over time: as the band's plating wears, it can look slightly warmer than the ring beside it, while platinum slowly takes on a soft patina of its own. If an exact match over the years matters to you, choose the same metal for both.
If you prefer identical metals, pair it with a white gold halo setting or another white gold design, and both rings will keep the same tone.
White metal shows color in a diamond more than yellow or rose gold does, so a diamond band looks its best with stones in the colorless or near colorless range. A slightly warm stone that would pass as white in yellow gold can show a hint of tint against bright rhodium. If it sits beside a center stone, keep the small diamonds close to its color, and browse white gold engagement rings if you are choosing both together.
Finish is the last choice. High polish shows off the bright rhodium surface best, while a brushed finish gives white gold a softer sheen of fine parallel lines that hides fine scratches.