Yes and no. Flower colours become deeper and the pigment can become more saturated when they dry. This means that the colours of your flowers, may change as they dry. Some yellows can turn more orange, reds turn to a darker burgundy, some whites dry to a beige, cream or off white tone, purples can result in darker tones, etc. If you have a specific question about a specific colour or flower, feel free to ask me any time.
There are some botanicals that don't dry well at all. For example, Hypericum berries always dry black, regardless of the colour of the berry (similarly to raisins). Succulents will not preserve as they shrivel up to nothing. Tulip petals shrink down to slivers. Thick stalked flowers that hold a lot of moisture are not going to be your friend here. If there is lots of moisture, that moisture is removed and it will shrivel and shrink. If you have these type of items in your bouquet and would like to include them in your preservation piece, we can always look into faux replicas to use in their place. Or they are items we can omit all together, this choice is totally yours!