how can I change RGB values according to percentage

I want to change RGB values according to the percentage. means 0% should show Red , 50% should green and 100% will Blue color.I am working on fastled.I tried like this but didnt get the best result.can anyone suggest some good stuf??

int R,G,B;
int p = percentage;
if(p >= 0 and p <= 50){
    R = abs(p - 100);
    G = p*2;
}
if(p > 50 and p <= 100){
    G = abs(p - 100);
    B = p*2;
}

>! also tried

R = abs(p-100);
G = p/2;
B = p;

leds[0] = CRGB(R,G,B);
FastLED.show();

From your problem statement, you probably want something like this which generates RGB colors counter-clockwise around the sRGB color gamut from red to blue.

#include <array>
#include <string>
#include <cmath>
#include <iostream>

std::array<uint8_t, 3> getcolorpercent(double percent)
{
    std::array<uint8_t, 3> rgb{};
    int segment{static_cast<int>(percent/25)};
    double percent_f = .01 * (percent - 25 * segment);
    double col0{ 1 }, col1{ 1 };
    if (segment % 2 == 0)
        col1 = sqrt(4 * percent_f);
    else
        col0 = sqrt(1 - 4 * percent_f);
    rgb[(segment / 2) % 3] = static_cast<uint8_t>(std::round(255*col0));
    rgb[(1 + segment / 2) % 3] = static_cast<uint8_t>(std::round(255 * col1));
    return rgb;
}

int main()
{
    auto print = [](const std::array<uint8_t, 3> rgb, std::string descr) {
        // note: 0+... is to convert uint8_t to int to precent interpreting as char
        std::cout << descr << " red:" << 0+rgb[0] << " green:" << 0+rgb[1] << " blue:" << 0+rgb[2] << '\n';
    };

    std::array<uint8_t, 3> rgb_red = getcolorpercent(0);
    std::array<uint8_t, 3> rgb_orange = getcolorpercent(15);
    std::array<uint8_t, 3> rgb_yellow = getcolorpercent(25);
    std::array<uint8_t, 3> rgb_cyan = getcolorpercent(75);
    std::array<uint8_t, 3> rgb_violet = getcolorpercent(130);
    print(rgb_red, "red=");
    print(rgb_orange, "orange=");
    print(rgb_yellow, "yellow=");
    print(rgb_cyan, "cyan=");
    print(rgb_violet, "violet=");
}

Output:

red= red:255 green:0 blue:0
orange= red:255 green:198 blue:0
yellow= red:255 green:255 blue:0
cyan= red:0 green:255 blue:255
violet= red:255 green:0 blue:228

This creates a (reversed) rainbow type from red to blue for 0% to 100%. Additionally, this has been expanded to allow percentages to exceed 100 which can be used to produces colors going from blue->violet->purple and back to red. Here's an image created from this going from percent 0 to 100: