Pour the clam juice into a small saucepan and heat to simmering. Keep hot over very low heat.
Heat the achiote oil over medium-high heat in a medium saucepan. Add the garlic, stirring to prevent sticking, and cook until lightly golden, about 2 minutes. Stir in the ham and cook until fragrant, 1 to 2 minutes. Add the orzo and stir until lightly toasted, about 2 minutes.
Pour enough hot clam juice into the skillet to cover the orzo by about 1/2-inch. Bring to a boil, then adjust the heat to medium-low. Continue cooking, adding small amounts of the hot clam juice to keep the orzo covered as necessary, until the pasta is tender but still firm, 6 to 8 minutes. Season with salt and pepper, to taste. The pasta should have a creamy consistency, but there should be little, if any, liquid left by the end of cooking. If a bit soupy, let stand for a minute or so. Transfer to a serving dish and garnish with the chopped parsley.
Heat the oil and annatto seeds in a small skillet over medium heat just until the seeds give off a lively, steady sizzle. Don't overheat the mixture or the seeds will turn black and the oil will turn a nasty green. Once they're sizzling, remove the pan from the heat and let stand until the sizzling stops. Strain and reserve in a jar with a tight-fitting lid at room temperature for up to 4 days.
*Achiote seeds are a deep orange seed with a nutty flavor. They are available in many supermarkets and almost all Latin markets.