While I personally believe that, at the 4-H level, as long as your show attire is clean, well fitted, safe, and appropriate, there should be no penalties against simpler clothing or points for flashier or obviously expensive clothing, the reality is that most judges, if not outright at least subconsciously, do sometimes favor the glitzier clothing. I have also seen the kids who just don't care and do Showmanship just because it it the required class (I don't know if this is national, but it is in my state.). I've done 4-H on a shoestring for years, English and Western, and seen superb performances, showmanship and rail, placed behind other competitors apparently based on clothing. While this practice may be appropriate at other shows, at 4-H the emphasis should always be on the kids, their ability to groom, handle, and show their projects. The necessity for clean and tidy clothes fall into this category, the necessity for brand name or rhinestone adorned clothing is not. The tendancy for judges to place according to tailor bills has strongly influenced my decision to switch to English, where a $60 hunt coat looks basically like a $600 hunt coat.
That being said, I would advise you to wear the flashier outfit. If you have blue slacks, try to find blue boots of a matching shade (makes a more streamlined outline). If you're brave, I have seen white boots that are made to dye the perfect shade (I've always been a black slacks and black boots gal for this reason, ha ha). Black boots work, but the contrast will draw the judge's eye to your feet. Gloves are another good idea, the same color as the sleeves of your top, again to minimize contrast and draw the eye away from your hands (Remember to leave them behind for your western rail classes!
) Unless your 4-H show requires a ASTM-SEI certified helmet for showmanship, a cowboy hat is a must. I would recommend cream felt to match your outfit.
Hope that helps! Good luck!