Name or hexcode are both fine.

0x0000FF, there is no other blue, everything else is a lie.

Weirdly, I kind of agree with 0x0000FF.

If you look at a color wheel:

...your blues start at about 150° hue, where they're still quite green. Then 180° is cyan, which is rather icy, so decidedly not warm. 210° is basically sky blue, still not very warm. 240° is 0x0000FF, which already borders on purple.

Obviously going towards purple, we're adding more red tones, which is generally meant with "warm", but yeah, it really starts to look purple quite quickly. Like, you could maybe still get away with 250°, depending on the surrounding colors.

If you do want to use 250° (or any other degree on this color wheel), find an HSL to RGB converter and stick the degree number into there as the 'hue', with saturation=100% and lightness=50%.
You can also fiddle with saturation lightness, if you want, but those settings give the most vibrant colors.