can a vehicle be seized if you owe arrears on child support in colorado even if you are making payments on it?Or a recreational vehicle or motorcycle?

If a party fails to make a child support payment when due, each unpaid obligation becomes an enforceable judgment automatically by law.  C.R.S. 14-10-122(1)(c).  Therefore, if you owe arrears, you have an enforceable judgment against you which can be used to collect including garnishing wages, placing a lien on property, and/or repossessing property.  It's not clear if you are making payments on the vehicle or the child support arrears.  If it is the vehicle - the fact that you are making payments on the vehicle is irrelevant to whether or not it can be repossessed.  If you are making payments on your child support arrears - if you have an agreement regarding satisfaction of the arrears through a payment plan, the recipient cannot take other action against you.  However, if you do not have an agreement, it is as stated above, they have an enforceable judgment against you.  I would suggest you discuss with an attorney to better understand your obligations and rights and to protect your property going forward.