Sus pantalones son anaranjados.
However, if there's no confusion over whose pants we're talking about, "los" is preferable to "sus."
There is two ways to say orange in Spanish, the meanings are different though. Naranja is Spanish for the kind of orange you eat and anaranjado is Spanish for the color orange.
Defequé mis pantalones
Pantalones de vestir
¿Dónde compraste tus pantalones?
Tu bailas sin pantalones.
tengo una naranja
Quieres naranja?
Yes. 'la naranja'= the orange 'una naranja'= an orange
Cat is "gato", orange (both the color and the fruit) is "naranja" with the j making an h sound. In Spanish the adjective follows the noun, so if you meant to say "the orange cat", you would say that as "el gato naranja." I am unaware of any kind of orange called a cat orange, but if there was one, the Spanish for it would likely be "la naranja del gato".
Tengo un gato en mis pantalones.
él está usando pantalones verdes.
el cerdo está en mis pantalones