RGB color from K temperature, port of https://tannerhelland.com/2012/09/18/convert-temperature-rgb-algorithm-code.html

LightsUtils.cs

internal static class LightsUtils
{
	public static int[] GetRgbFromTemperature(double temperature)
	{
		// Temperature must fit between 1000 and 40000 degrees.
		temperature = MathUtils.Clamp(temperature, 1000, 40000);

		// All calculations require temperature / 100, so only do the conversion once.
		temperature /= 100;

		// Compute each color in turn.
		int red, green, blue;

		// First: red.
		if (temperature <= 66)
		{
			red = 255;
		}
		else
		{
			// Note: the R-squared value for this approximation is 0.988.
			red = (int)(329.698727446 * (Math.Pow(temperature - 60, -0.1332047592)));
			red = MathUtils.Clamp(red, 0, 255);
		}

		// Second: green.
		if (temperature <= 66)
		{
			// Note: the R-squared value for this approximation is 0.996.
			green = (int)(99.4708025861 * Math.Log(temperature) - 161.1195681661);
		}
		else
		{
			// Note: the R-squared value for this approximation is 0.987.
			green = (int)(288.1221695283 * (Math.Pow(temperature - 60, -0.0755148492)));
		}

		green = MathUtils.Clamp(green, 0, 255);

		// Third: blue.
		if (temperature >= 66)
		{
			blue = 255;
		}
		else if (temperature <= 19)
		{
			blue = 0;
		}
		else
		{
			// Note: the R-squared value for this approximation is 0.998.
			blue = (int)(138.5177312231 * Math.Log(temperature - 10) - 305.0447927307);
			blue = MathUtils.Clamp(blue, 0, 255);
		}

		return new[] { red, green, blue };
	}
}

MathUtils.cs

public static class MathUtils
{
    public static T Clamp<T>(T value, T min, T max)
        where T : IComparable<T>
    {
        if (value.CompareTo(min) < 0)
        {
            value = min;
        }
        else if (value.CompareTo(max) > 0)
        {
            value = max;
        }

        return value;
    }
}