Red and yellow flags
5 countries have a red and yellow flag, with no other significant colour: Kyrgyzstan, Montenegro, North Macedonia, Spain, Vietnam. 44 other flags also contain these colours, plus others.
Red and yellow, plus other colours
Andorra
Armenia
Belgium
Benin
Bolivia
Brunei
Cameroon
Central African Republic
Chad
Colombia
Comoros
Democratic Republic of the Congo
Dominica
Ecuador
Eswatini
Ethiopia
Germany
Ghana
Grenada
Guinea
Guinea-Bissau
Guyana
Kiribati
Lithuania
Mali
Mauritius
Moldova
Mongolia
Mozambique
Myanmar
Papua New Guinea
Republic of the Congo
Romania
Saint Kitts and Nevis
São Tomé and Príncipe
Senegal
Seychelles
Sri Lanka
Timor-Leste
Togo
Uganda
Vanuatu
Venezuela
Zimbabwe
Other colour combinations
red, white and bluered and whitered, green and yellowred, white and greenred, blue and yellowwhite and blueblue and yellowred, white, green and blackred and greenred, yellow and blackblue, green and yellowwhite, blue and greenwhite, green and orangered, white and blackred, white, blue and greenred and bluered and blackred, white, blue and blackred, blue and greenred, white, green and yellowwhite, blue and blackred, blue, green and yellowred, green and blackwhite and greenred, green, yellow and black