The flag most people mean by “yellow, blue and red” is the national flag of Colombia, which has three horizontal stripes: a thick yellow band on top (half the flag’s height), then equal blue and red bands below.

However, several countries use the same three colors in different layouts:

  • Colombia – Horizontal stripes, yellow on top (double height), then blue, then red.
  • Venezuela – Horizontal yellow, blue, red stripes of equal size, with stars in the blue band on the current flag.
  • Ecuador – Same basic horizontal yellow–blue–red as Colombia and Venezuela, but with a national coat of arms in the center.
  • Romania – Vertical blue, yellow, red stripes.
  • Chad – Almost identical to Romania (vertical blue, yellow, red), but with a slightly different shade of blue.
  • Moldova – Vertical blue, yellow, red with the national coat of arms (an eagle and shield) in the yellow center stripe.

So if your flag is:

  • Horizontal with a very thick yellow stripe on top: it is likely Colombia.
  • Horizontal equal stripes, often with stars in the blue: likely Venezuela (or Ecuador if there is a detailed coat of arms).
  • Vertical stripes with no symbol: usually Romania or Chad.
  • Vertical stripes with an eagle/shield in the middle: Moldova.

If you tell me whether the stripes are vertical or horizontal and if there’s any emblem in the center, I can narrow it down to one specific country.