What you need, the colours to be permanent and water/heat-resistant, glazing is the right way to go. JONQUIL YELLOW glaze will display little specks, tints, shades and uneven tones

JONQUIL YELLOW is Cone 06 oxidation aventurine glaze that looks like high fired reduction stoneware glazes. Aventurine effects and other reduction surfaces are achieved without the cost or trouble of high fire reduction. It's an unusual and interesting glaze and gives best results when applied thickly and fired on flat surfaces. On vertical surfaces and thinner application, the results will vary. The color in the clay will not show through where there is texture but adds dimension to the glaze. Because of this effect, these glazes will look completely different.

How to use Artistic Glazes (Aventurines): 

Liquid glaze is perfect for brush on. It should be coated 2-3 times with a soft brush after the first fire. After drying please fire between 940-1000°C. Shake and stir very well prior to use. If the glaze becomes thickened over time simply add water and stir thoroughly.

Dry glaze is to be dissolved in water to a thick paste which should be thinned to the proper density. Each glaze is recommended to be tested with various layers on the body concerned and under determined conditions.  The mixing of the glazes is possible in order to change color shade, melting properties or to achieve some artistic effects. Sometimes the glaze coat can crawl due to the presence of dust, grease or dirt on the bisque. Glazed pieces have to be well dried before the firing. The firing temperature should correspond to the given data. 

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Quantity: 40 g. (1,41 oz.) 
Firing temperature: 940-1000°C (1700-1830° F) (up to Cone 06) 
Surface: matt
Luminescence: cover (opaque)
Lead content: lead-free, 0%

What is a glaze, what is antiquing and other Q/A for painting and glazing can be found in the section: Paint and Glaze.